Because of the Tibet power grid is in the early stage of development and its AC system is very weak, the connection of Qinghai-Tibet DC transmission line will cause the situation of weak system with big DC power and the unblock mode with 10 % rated power not satisfying the systems operation requirement. This paper studied the minimum start-stop power and method for the Qinghai-Tibet DC project in order to make system operation safe and stable, and proposed monopole and bipolar start-stop methods. The special requirements of AC smoothing reactor and converter valve were also put forward for the minimum start-stop power. The DC start-stop method of unlock/block with 10% rated current and 25% rated voltage can implement monopole unlock/block with 2.5% rated power and reduce the impact of DC start-stop on the AC systems frequency. This start-stop method can ensure the system operation safe and stable, which has been successfully applied in the Qinghai-Tibet DC interconnection project.