<a-form-item label="产品特性" class="am-enter_form_item">
                <a-select mode="tags"
                          class="am-enter-select"
                          placeholder="选择或填写2~4个标签（限制2~4个字）"
                          showArrow
                          :max-tag-count="4"
                          :max-tag-text-length="4"
                          v-decorator="['productFeature', { rules: [{ required: true, message: '请输入产品特性'},{validator: selectTagChange}] }]"
                >
                  <a-select-option value="额度高">额度高</a-select-option>
                  <a-select-option value="利率低">利率低</a-select-option>
                  <a-select-option value="期限长">期限长</a-select-option>
                  <a-select-option value="放款快">放款快</a-select-option>
                  <a-select-option value="极速审批">极速审批</a-select-option>
                </a-select>
              </a-form-item>

在methods中写

selectTagChange: function (rule, value, callback) {
        var status = true
        if (!value) {//特别注意在为空时校验规则已写，所以这儿照样callback()，不然不会执行空时的校验
          callback()
        } else {
          if (value.length <= 4 && value.length >= 2) {
            value.map(function (item) {
              if (item.length > 4 || item.length < 2) {
                status = false
                return
              }
            })
            if (!status) {
              callback('选择或填写2~4个标签（限制2~4个字）')
            } else {
              callback()
            }
          } else {
            callback('选择或填写2~4个标签（限制2~4个字）')
          }
        }
      },