The fault current limiter is based on fast switching, high-speed sampling and fault identification control protection system, which is able to quickly string the current limiting reactance into the fault circuit after the system fault, suppressing the short-circuit current level, and providing a new overall solution for guaranteeing the transient safety of the system. This paper analyzes the related effects of fault current limiter access on the main transformer protection, simulates the actual project as an example, and analyzes the current fluctuation characteristics after the fault current limiter access, and the calculation shows that the fault current limiter access has a slight effect on the differential sensitivity. This paper also analyzes the influence of impedance circle and impedance sensitivity angle of medium voltage side impedance protection after fault current limiter access, and the calculation shows that the impedance protection value setting of medium voltage side should be adjusted, but the impedance protection sensitivity angle is not affected.