<ElDatePicker ref="datePickerRef" />
mounted() {
  console.log(this.$refs.datePickerRef.$el.querySelector('.el-input__inner'));
}

你是指在Composition API中吧，因为你已经在Options API中了，这里假设你正在使用TypeScript：
    <script setup lang="ts">
      import { onMounted, ref } from 'vue';
      import { ElDatePicker } from './你的/组件路径/component.vue';
      const datePickerRef = ref<typeof ElDatePicker | null>(null);
      onMounted(() => {
        if (datePickerRef.value) {
            console.log(datePickerRef.value.$el.querySelector('.el-input__inner'));
        }
      });
    </script>
    <template>
      <ElDatePicker ref="datePickerRef" />
    </template>
如果你没有使用TypeScript：
    <script setup>
      import { onMounted, ref } from 'vue';
      const datePickerRef = ref(null);
      onMounted(() => {
        if (datePickerRef.value) {
            console.log(datePickerRef.value.$el.querySelector('.el-input__inner'));
        }
      });
    </script>
    <template>
      <ElDatePicker ref="datePickerRef" />
    </template>

    <script setup>
    import { ref, onMounted } from "vue";
    const myReference = ref(null);
    onMounted(() => {
      console.log(myReference.value); <-- 这将输出一个 DOM 节点
    })
    </script>
    <template>
      <h1 ref="myReference">我现在可以访问 DOM 引用了</h1>
    </template>