Because of its excellent reactive power output characteristics，fast response and small footprint，static synchronous compensator（STATCOM）has been more and more widely used in power system.At present，cascade multilevel converter and modular multilevel converter（MMC）are the most possible solutions of STATCOM for transmission system.A contrast study of two schemes is conducted in terms of equipment constitutes，control performance，grounding method and fault ride-through capability，and a conclusion is obtained that cascade scheme is more suitable than MMC scheme for STATCOM used in transmission system.