可能原因是 composer 的安装包网址是国外镜像所致,被长城防火墙屏蔽了。可执行以下命令来解决:composer config -g repo.packagist composer https://packagist.phpcomposer.com
composer config -g repo.packagist composer https://packagist.phpcomposer.com
可更改安装包的全局镜像网址,然后再执行你的操作。