感谢你们的支持.

<i>$getdetails= mysql_fetch_array(mysql_query("SELECT * FROM `wp_users` WHERE `ID`='$user_id'"));
$username=$getdetails['user_login'];


$creds = array();
$creds['user_login'] = $username;
$creds['user_password'] = $password;
$creds['remember'] = true;

    $user = wp_signon( $creds, false );
    if ( is_wp_error($user) ){
        echo $user->get_error_message();
    }else{
        wp_redirect( home_url() );
    }