使用插件autoresize

window.tinymce.init({
        selector: `#${this.tinymceId}`,
        language: 'zh_CN',
        height: this.height,
        body_class: 'panel-body ',
        object_resizing: false,
        toolbar: this.toolbar.length > 0 ? this.toolbar : toolbar,
        menubar: this.menubar,
        plugins: 'autoresize',
        autoresize_bottom_margin: 50, 
        autoresize_max_height: 650, // 编辑区域的最大高
        autoresize_min_height: 350, //编辑区域的最小高度
        autoresize_on_init: true,
        autoresize_overflow_padding: 50,
        end_container_on_empty_block: true  
      })

详细信息参考
https://www.tinymce.com/docs/plugins/autoresize/