Generator voltage-class-reduction scheme is a kind of efficient and economical approach to solve the imbalance between the increasing local-demand and generator capacity. Whereas, the generator voltage-class-reduction scheme will decrease the short-circuit impedance on the original network side (high-voltage side), in the meanwhile, the short-circuit current in the quasi-accessed networks side (low-voltage side) will be increased, making the short-circuit current exceed the interrupting capacity of the circuit breaker in low-voltage side and affecting the safe operation of the power grid seriously. This paper mainly proposes a novel method of calculating the short-circuit current and a mathematical model in the generator voltage-class-reduction scheme to research the relationship between the variation of short-circuit and the parameters of the generator. The method has been applied to select the generator voltage-class-reduction schemes in Hunan power grids. According to the results of the simulation and application, the method of short-circuit current analysis in this paper can accurately and directly reflect the changing of the short-circuit current in generator voltage-class-reduction schemes, which provides a guarantee for the power grid running with safety and stability. This work is supported by Youth Fund of National Natural Science Foundation of China (No.51607011) and Science and Technology Project of State Grid Corporation of China (No. 5216D114000A).