diff --git a/components/_util/createContext.ts b/components/_util/createContext.ts
new file mode 100644
index 000000000..aa68a11e8
--- /dev/null
+++ b/components/_util/createContext.ts
@@ -0,0 +1,17 @@
+import { inject, provide } from 'vue';
+
+function createContext<T>() {
+  const contextKey = Symbol('contextKey');
+  const useProvide = (props: T) => {
+    provide(contextKey, props);
+  };
+  const useInject = () => {
+    return inject(contextKey, undefined as T) || ({} as T);
+  };
+  return {
+    useProvide,
+    useInject,
+  };
+}
+
+export default createContext;
diff --git a/components/button/button-group.tsx b/components/button/button-group.tsx
index fd543d9ff..19c2bf42a 100644
--- a/components/button/button-group.tsx
+++ b/components/button/button-group.tsx
@@ -2,9 +2,10 @@ import { computed, defineComponent } from 'vue';
 import { flattenChildren } from '../_util/props-util';
 import useConfigInject from '../_util/hooks/useConfigInject';
 
-import type { ExtractPropTypes, PropType } from 'vue';
+import type { ExtractPropTypes, PropType, ComputedRef } from 'vue';
 import type { SizeType } from '../config-provider';
-import UnreachableException from '../_util/unreachableException';
+import devWarning from '../vc-util/devWarning';
+import createContext from '../_util/createContext';
 
 export const buttonGroupProps = () => ({
   prefixCls: String,
@@ -14,12 +15,17 @@ export const buttonGroupProps = () => ({
 });
 
 export type ButtonGroupProps = Partial<ExtractPropTypes<ReturnType<typeof buttonGroupProps>>>;
-
+export const GroupSizeContext = createContext<{
+  size: ComputedRef<SizeType>;
+}>();
 export default defineComponent({
   name: 'AButtonGroup',
   props: buttonGroupProps(),
   setup(props, { slots }) {
     const { prefixCls, direction } = useConfigInject('btn-group', props);
+    GroupSizeContext.useProvide({
+      size: computed(() => props.size),
+    });
     const classes = computed(() => {
       const { size } = props;
       // large => lg
@@ -37,7 +43,7 @@ export default defineComponent({
           break;
         default:
           // eslint-disable-next-line no-console
-          console.warn(new UnreachableException(size).error);
+          devWarning(!size, 'Button.Group', 'Invalid prop `size`.');
       }
       return {
         [`${prefixCls.value}`]: true,
diff --git a/components/button/button.tsx b/components/button/button.tsx
index d5a1a3960..658a42ce0 100644
--- a/components/button/button.tsx
+++ b/components/button/button.tsx
@@ -18,13 +18,14 @@ import LoadingIcon from './LoadingIcon';
 
 import type { ButtonType } from './buttonTypes';
 import type { VNode, Ref } from 'vue';
+import { GroupSizeContext } from './button-group';
 
 type Loading = boolean | number;
 
 const rxTwoCNChar = /^[\u4e00-\u9fa5]{2}$/;
 const isTwoCNChar = rxTwoCNChar.test.bind(rxTwoCNChar);
 
-function isUnborderedButtonType(type: ButtonType | undefined) {
+function isUnBorderedButtonType(type: ButtonType | undefined) {
   return type === 'text' || type === 'link';
 }
 export { buttonProps };
@@ -37,7 +38,7 @@ export default defineComponent({
   // emits: ['click', 'mousedown'],
   setup(props, { slots, attrs, emit }) {
     const { prefixCls, autoInsertSpaceInButton, direction, size } = useConfigInject('btn', props);
-
+    const { size: groupSize } = GroupSizeContext.useInject();
     const buttonNodeRef = ref<HTMLElement>(null);
     const delayTimeoutRef = ref(undefined);
     let isNeedInserted = false;
@@ -76,7 +77,7 @@ export default defineComponent({
       const pre = prefixCls.value;
 
       const sizeClassNameMap = { large: 'lg', small: 'sm', middle: undefined };
-      const sizeFullname = size.value;
+      const sizeFullname = groupSize?.value || size.value;
       const sizeCls = sizeFullname ? sizeClassNameMap[sizeFullname] || '' : '';
 
       return {
@@ -85,7 +86,7 @@ export default defineComponent({
         [`${pre}-${shape}`]: shape !== 'default' && shape,
         [`${pre}-${sizeCls}`]: sizeCls,
         [`${pre}-loading`]: innerLoading.value,
-        [`${pre}-background-ghost`]: ghost && !isUnborderedButtonType(type),
+        [`${pre}-background-ghost`]: ghost && !isUnBorderedButtonType(type),
         [`${pre}-two-chinese-chars`]: hasTwoCNChar.value && autoInsertSpace.value,
         [`${pre}-block`]: block,
         [`${pre}-dangerous`]: !!danger,
@@ -132,7 +133,7 @@ export default defineComponent({
 
     watchEffect(() => {
       devWarning(
-        !(props.ghost && isUnborderedButtonType(props.type)),
+        !(props.ghost && isUnBorderedButtonType(props.type)),
         'Button',
         "`link` or `text` button can't be a `ghost` button.",
       );
@@ -149,7 +150,7 @@ export default defineComponent({
       const { icon = slots.icon?.() } = props;
       const children = flattenChildren(slots.default?.());
 
-      isNeedInserted = children.length === 1 && !icon && !isUnborderedButtonType(props.type);
+      isNeedInserted = children.length === 1 && !icon && !isUnBorderedButtonType(props.type);
 
       const { type, htmlType, disabled, href, title, target, onMousedown } = props;
 
@@ -202,7 +203,7 @@ export default defineComponent({
         </button>
       );
 
-      if (isUnborderedButtonType(type)) {
+      if (isUnBorderedButtonType(type)) {
         return buttonNode;
       }
 
diff --git a/components/button/style/mixin.less b/components/button/style/mixin.less
index 96efadc8d..084ecaa5b 100644
--- a/components/button/style/mixin.less
+++ b/components/button/style/mixin.less
@@ -210,28 +210,6 @@
   .@{btnClassName}-icon-only {
     font-size: @font-size-base;
   }
-  // size
-  &-lg > .@{btnClassName},
-  &-lg > span > .@{btnClassName} {
-    .button-size(@btn-height-lg; @btn-padding-horizontal-lg; @btn-font-size-lg; 0);
-  }
-  &-lg .@{btnClassName}.@{btnClassName}-icon-only {
-    .square(@btn-height-lg);
-    padding-right: 0;
-    padding-left: 0;
-  }
-  &-sm > .@{btnClassName},
-  &-sm > span > .@{btnClassName} {
-    .button-size(@btn-height-sm; @btn-padding-horizontal-sm; @font-size-base; 0);
-    > .@{iconfont-css-prefix} {
-      font-size: @font-size-base;
-    }
-  }
-  &-sm .@{btnClassName}.@{btnClassName}-icon-only {
-    .square(@btn-height-sm);
-    padding-right: 0;
-    padding-left: 0;
-  }
 }
 // Base styles of buttons
 // --------------------------------------------------