In a ground test, it is hard to conduct a full-physical simulation of function modules of a space station because of the great volume of space, the difficulties of weightlessness simulation and the huge cost. A test method based on the equivalent inertia simulation is proposed, which makes the volume of load inertia much smaller and reduces the difficulties of its micro-gravity space environment simulation. Inertia simulator, a mechanical mechanism mainly composed of gas bearings and a planet-gear increaser, is designed, and a mathematic model of the equivalent load of the inertia simulator based on the equivalent dynamics theory is established. Finally, simulation results show that the method is effective and can achieve the same joint torque loads of the space station redocking manipulator just as in space translocation. The relative errors of load torque of wrist joint and shoulder joint, respectively, are less than 4.61% and 1.33% and the maximum simulation errors of rotation inertia of wrist joint and shoulder joint, respectively, are 4.52% and 1.03%, which shows that the method can achieve a valid load bearing performance test of the space redocking manipulator.