我认为你不能禁用大尺寸，但是你可以设置它的宽度和高度与中等尺寸相同。它在设置→媒体下

你可以通过强制WordPress不显示全尺寸选项来达到这个效果。创建大小单选按钮的函数在wp-admin/includes/media.php中，名为image_size_input_fields。
据我所知，这个函数没有filter或action钩子，但是调用它的函数（image_attachment_fields_to_edit）有一个filter钩子attachment_fields_to_edit。
所以基本上我们可以使用filter钩子来用我们自己的函数覆盖这两个函数，我们只会做很小的修改。
这将在标准的functions.php文件中工作，或者我想您可以将其合并到插件中。
首先，添加新筛选器：

add_filter('attachment_fields_to_edit', 'MY_image_attachment_fields_to_edit', 11, 2);

接下来我们创建两个函数，在这个例子中，我只是在函数名前加上了前缀MY_：

function MY_image_attachment_fields_to_edit($form_fields, $post) {
 if ( substr($post->post_mime_type, 0, 5) == 'image' ) {
  $alt = get_post_meta($post->ID, '_wp_attachment_image_alt', true);
  if ( empty($alt) )
   $alt = '';

  $form_fields['post_title']['required'] = true;

  $form_fields['image_alt'] = array(
   'value' => $alt,
   'label' => __('Alternate text'),
   'helps' => __('Alt text for the image, e.g. “The Mona Lisa”')
  );
  
  $form_fields['align'] = array(
   'label' => __('Alignment'),
   'input' => 'html',
   'html'  => image_align_input_fields($post, get_option('image_default_align')),
  );

  $form_fields['image-size'] = MY_image_size_input_fields( $post, get_option('image_default_size', 'medium') );

 } else {
  unset( $form_fields['image_alt'] );
 }
 
 return $form_fields;
}

与普通WordPress函数相比，这里唯一的变化是我们调用MY_image_size_input_fields而不是image_size_input_fields。
现在执行实际隐藏的函数是：

function MY_image_size_input_fields( $post, $check = '' ) {

  // get a list of the actual pixel dimensions of each possible intermediate version of this image
  /* $size_names = array('thumbnail' => __('Thumbnail'), 'medium' => __('Medium'), 'large' => __('Large'), 'full' => __('Full size')); */
  $size_names = array('thumbnail' => __('Thumbnail'), 'medium' => __('Medium'), 'large' => __('Large'));

  if ( empty($check) )
   $check = get_user_setting('imgsize', 'medium');
   
   echo '<pre>'; print_r($check); echo '</pre>';
   

  foreach ( $size_names as $size => $label ) {
   
   $downsize = image_downsize($post->ID, $size);
   $checked = '';

   // is this size selectable?
   $enabled = ( $downsize[3] || 'large' == $size );
   $css_id = "image-size-{$size}-{$post->ID}";
   // if this size is the default but that's not available, don't select it
   if ( $size == $check ) {
    if ( $enabled )
     $checked = " checked='checked'";
    else
     $check = '';
   } elseif ( !$check && $enabled && 'thumbnail' != $size ) {
    // if $check is not enabled, default to the first available size that's bigger than a thumbnail
    $check = $size;
    $checked = " checked='checked'";
   }

   $html = "<div class='image-size-item'><input type='radio' " . ( $enabled ? '' : "disabled='disabled' " ) . "name='attachments[$post->ID][image-size]' id='{$css_id}' value='{$size}'$checked />";

   $html .= "<label for='{$css_id}'>$label</label>";
   // only show the dimensions if that choice is available
   if ( $enabled )
    $html .= " <label for='{$css_id}' class='help'>" . sprintf( __("(%d&nbsp;&times;&nbsp;%d)"), $downsize[1], $downsize[2] ). "</label>";

   $html .= '</div>';

   $out[] = $html;
   
  }

  return array(
   'label' => __('Size'),
   'input' => 'html',
   'html'  => join("\n", $out),
  );
}

在最后一个函数中，只有两点改变。在顶部，我们去掉了$size_names数组定义中对'Full Size'的引用。然后，我们修改了$enabled = ( $downsize[3] || 'large' == $size );行。我们只是用'large' == $size替换了'full' == $size。
下面是结果的截图：