我想你在找img_caption_shortcode_width 过滤器，在img_caption_shortcode():

/**
 * Filters the width of an image\'s caption.
 *
 * By default, the caption is 10 pixels greater than the width of the image,
 * to prevent post content from running up against a floated image.
 *
 * @since 3.7.0
 *
 * @see img_caption_shortcode()
 *
 * @param int    $width    Width of the caption in pixels. To remove this inline style,
 *                         return zero.
 * @param array  $atts     Attributes of the caption shortcode.
 * @param string $content  The image element, possibly wrapped in a hyperlink.
 */
$caption_width = apply_filters( \'img_caption_shortcode_width\', $width, $atts, $content );

add_filter( \'img_caption_shortcode_width\', \'__return_zero\' );