The powerful apparatus to compensate reactive power, STATCOM, uses voltage source converter which is consist of fully-controlled switches, response rapidly and alter flexible. This paper mixes phase shifted carrier PWM and selected harmonic elimination PWM together as a new control method both for character and requirement of power system, on the base of analysis of multi-level inverter technology, also find the solution for DC steady state at the same time. It's proved feasible and effective by the result of simulation.