Low voltage ride-though test of wind power generation system is carried out before connected with grid, it is necessary to use special voltage sag simulated generator for this test. A transformer typed voltage sag generator special for wind power system is researched, different type faults and voltage sag deep can be simulated, voltage sag last time is also adjusted. In order to ensure safe and stable operation of voltage sag test system, complete breakdown protection schemes are designed. Simulation and spot test shows this voltage sag generator is satisfied with practical engineering application, which provides implementation scheme and reference of voltage sag generator for wind power generation system low voltage ride through test.