页面modal 代码：

<a-modal v-drag-modal title="弹窗" v-model="isShow">
	...
</a-modal>

如要全局使用拖拽功能
在main.js中定义（全局可用）

Vue.directive('drag-modal', (el, bindings, vnode) => {
  Vue.nextTick(() => {
    let { visible, destroyOnClose } = vnode.componentInstance
    // 防止未定义 destroyOnClose 关闭弹窗时dom未被销毁，指令被重复调用
    if (!visible) return
    let modal = el.getElementsByClassName('ant-modal')[0]
    let header = el.getElementsByClassName('ant-modal-header')[0]
    let left = 0
    let top = 0

    // 未定义 destroyOnClose 时，dom未被销毁，关闭弹窗再次打开，弹窗会停留在上一次拖动的位置
    if (!destroyOnClose) {  
      left = modal.left || 0
      top = modal.top || 0
    }
    // top 初始值为 offsetTop
    top = top || modal.offsetTop
    header.onmousedown = e => {
      let startX = e.clientX;
      let startY = e.clientY;
      header.left = header.offsetLeft;
      header.top = header.offsetTop;
      el.onmousemove = event => {
        let endX = event.clientX;
        let endY = event.clientY;
        modal.left = header.left + (endX - startX) + left;
        modal.top = header.top + (endY - startY) + top;
        modal.style.left = modal.left + 'px'
        modal.style.top = modal.top + 'px'
      }
      el.onmouseup = event => {
        left = modal.left
        top = modal.top
        el.onmousemove = null;
        el.onmouseup = null; 
        header.releaseCapture && header.releaseCapture();
      }
      header.setCapture && header.setCapture();
    }  
  })
})

或者是在当前vue实例中定义 （当前页面可用）

import Vue from 'vue'
export default {
	data(){
		return {
			...
		}
	},
	directives: {
	  'drag-modal'(el, bindings, vnode){
	    Vue.nextTick(() => {
		  // 内容同上 ...
	    })
	  }
	},
}