The invention belongs to the technical field of airplane simulating tests and particularly relates to a flap rudder surface servo loading mechanism used for conducting servo loading on the flap rudder surface when an airplane ground semi-physical test is conducted. In the airplane ground semi-physical test, a series of control system and hydraulic system ground semi-physical tests need to be conducted. When loading is conducted on the flap rudder surface, the method that weights are hung on the flap rudder surface is adopted generally to simulate a load, so that a real-time aerodynamic load and the like borne by the flap rudder surface cannot be simulated. The invention provides a flap rudder surface servo loading fixture. The servo loading fixture mechanism is composed of mechanical, electric and hydraulic elements. The automatic loading degree is high, the aerodynamic load of the flap rudder surface can be simulated realistically, the accuracy and consistency of test data are improved, and the test efficiency and quality can be improved.