你应该加入save_post 并使用wp_set_object_terms():

// Add an action to run on post save
add_action( \'save_post\', \'set_genre_on_save\' );
function set_genre_on_save( $post_id ){
    // Check the post type
    if (is_single(\'tvseries\')) {
        // Get the custom field data
        $custom_field_data = get_post_custom( $post_id );
        // Check if there is any genres entered in the metabox
        if (isset($custom_box_data[\'genre\'])) {
            // Save the genre data (separated by comma) into an array
            $genre_array = explode( \',\', $custom_box_data[\'genre\'] );
            //Set the array values to lower case
            foreach ($genre_array as $genre){
                $genre = strtolower($genre);
            }
            // Set the categories for these genres
            wp_set_object_terms( $post_id, $genre_array, \'category\' );
        }
    }
}

请注意，这只是一个示例，因为您没有发布任何代码。您可能需要更改某些值，例如genres 以匹配自定义字段/帖子类型。