The invention relates to a simulation system and a control protecting method thereof, which belong to the field of power systems and particularly relates to a cascade multi-terminal extra-high voltage direct current simulation system and a control protection method thereof. The simulation system comprises a primary simulation platform and a control protection system, wherein the primary simulation platform forms cascade multi-terminal extra-high voltage direct current by adopting digital/analogue mixing simulation equipment; the control protection system forms cascade multi-terminal extra-high voltage direct current power transmission on the basis of dual-terminal extra-high voltage direct current power transmission control protection; and the primary simulation platform is connected with the control protection system through an analogue quantity and digital quantity interface and comprises an alternating current system and a direct current system which are sequentially connected. According to the scheme provided by the invention, the simulation result has favorable credibility and reliability.