Mr Green won't go home until he finishes the work.

until 引导的时间状语从句,主句用一般将来时 （ Mr Green won't go home） 从句中用一般现在时,即‘主将从现’.从句主语是he 第三人称单数,故用finishes (类似用法的还有：if ,when ,as soon as 等）