The invention discloses a double-fed wind generator system short-circuit current calculation method under low-voltage crossing. A fault process of a double-fed wind turbine generator system is divided into a process before low-voltage crossing control starts and a process after the low-voltage crossing control starts. Double-fed wind turbine generator system fault calculation equivalent models of the two processes are established, and by use of an electrical network method, power frequency short-circuit currents at any positions of a power system comprising the double-fed wind turbine generator system and short-circuit full currents output by the double-fed wind turbine generator system are calculated. According to the invention, a relation between fault initial voltages under a new low-voltage crossing requirement and a low-voltage crossing instruction value of the double-fed wind turbine generator system is taken into consideration, influences exerted by power grid transient voltages due to change of reactive power output by the double-fed wind turbine generator system on output short-circuit currents can also be taken into account, the power frequency short-circuit currents at any positions of the power system and the short-circuit full currents output by the double-fed wind turbine generator system can be calculated, and the demands for protective setting and equipment type selection of the power system are satisfied.