已解决。。我分两步完成，效果非常好！

if(isset ($_POST[\'new_title\']) && $_POST[\'new_title\'] != "")
                            {

                                $post_type = get_post_type( get_the_ID() );
                                $id_post = get_the_ID();                
                                $title = get_field(\'titre\');

                                $postInfo = array(
                                    \'post_type\' => $post_type,
                                    \'ID\' => $id_post
                                );

                                $id = wp_update_post($postInfo);

                                update_post_meta( $id, \'titre\', $_POST[\'new_title\'] );

                                $new_title = $_POST[\'new_title\'];

                                $new_elem = array(
                                    \'post_type\' => $post_type,
                                    \'ID\' => $id_post,
                                    \'post_title\' => $new_title
                                );

                                wp_update_post($new_elem);

                            }