You have a pre-existing .ssh/config or /etc/ssh/ssh_config file, possibly with a GSSAPIKeyExchange no setting that was previously required for El Capitan (Mac OS 10.11)
$ git clone git@github.com:EverChan6/meetingDemo.gitCloning into ‘meetingDemo’…packet_write_wait: Connection to 52.74.223.119 port 22: Broken pipe // <==就是它!!!fatal: Could not read from …