将下列代码丢到当前主题的functions.php文件中。

add_filter( 'wp_authenticate', 'ten_no_admin_user' );
function ten_no_admin_user( $user ) {
	if ( $user == 'admin' ) {
		exit;
	}
}

add_filter( 'sanitize_user', 'ten_sanitize_user_no_admin', 10, 3 );
function iten_sanitize_user_no_admin( $username, $raw_username, $strict ) {
	if ( $raw_username == 'admin' || $username == 'admin' ) {
		exit;
	}
	return $username;
}