This paper uses the soft switch technology, power devices under the condition of zero voltage or zero current conduction or shut off, it can effectively reduce the switching loss,and theoretically zero switching loss.Soft switch technology of switch power supply theory analysis, this paper analyzes the soft switch of the operational modal ZVZCS, lagging advanced arm and arm control mode as well as the advance, the problem such as lag bridge arm of the dead zone formation. Keywords-soft switch;zero voltage;zero curren;switching