在当前主题的functions.php文件最下面添加以下代码:

//添加图床上传按钮
add_action('media_buttons', 'add_my_media_button');
function add_my_media_button()
{
    echo '<input id="karma617_up_img" type="file" accept="image/*" multiple="multiple"/>
          <label for="karma617_up_img" id="up_img_label" class="button"> 上传图片到图床</label>
          ';
?>
    <style type="text/css">
        #karma617_up_img {
            display: none;
        }

        #up_img_label:before {
            font-family: dashicons;
            content: "\f128";
        }
    </style>
    <script type="text/javascript">
        jQuery('#karma617_up_img').off("change").change(function() {
            window.wpActiveEditor = null;
            for (var i = 0; i < this.files.length; i++) {
                var f = this.files[i];
                if (!/image\/\w+/.test(f.type)) {
                    alert('请选择图片文件(png | jpg | gif)');
                    return
                }
                var formData = new FormData();
                formData.append('images', f); //提示:这里的images是api的文件请求参数名
                jQuery.ajax({
                    async: true,
                    crossDomain: true,
                    url: 'xxxxx', //提示:这里是上传接口地址
                    type: 'POST',
                    processData: false,
                    contentType: false,
                    dataType: 'json',
                    data: formData,
                    beforeSend: function(xhr) {
                        jQuery('#up_img_label').html('<i class="fa fa-spinner rotating" aria-hidden="true"></i> Uploading...');
                    },
                    success: function(res) {
                        console.log(res.data.imageURLs[0])
                        wp.media.editor.insert('<a href=' + res.data.url + '><img src=' + res.data.url + ' ></img></a>'); //提示:res.data.url 这里的url是返回的图片字段
                        jQuery("#up_img_label").html('<i class="fa fa-check" aria-hidden="true"></i> 上传成功,继续上传');
                    },
                    error: function() {
                        jQuery("#up_img_label").html('<i class="fa fa-times" aria-hidden="true"></i> 上传失败,重新上传');
                    }
                });
            }
        });
    </script>
<?php
}