laravel new blog 后访问提示 Warning: require

错误提示
Warning: require(D:\WWW\laravel\bootstrap/../vendor/autoload.php): failed to open stream: No such file or directory in D:\WWW\laravel\bootstrap\autoload.php on line 17

Fatal error: require(): Failed opening required 'D:\WWW\laravel\bootstrap/../vendor/autoload.php' (include_path='.;C:\xampp\php\PEAR') in D:\WWW\laravel\bootstrap\autoload.php on line 17