The present invention discloses an inertia measurement apparatus rocket sled overload test method based on a 9 km orbit. According to the method, three rich positive direction-negative direction overloads are provided in one test process; in each alternation process, an engine ignites to provide a heading overload at the starting stage of the test, and a heading positive direction acceleration is generated, wherein the process is the active segment; when the work of the engine stops, frictional resistance and air resistance of the orbit are applied on the rocket sled, and a heading negative direction acceleration is generated, wherein the process is the free gliding segment; when the rocket sled enters a water brake region, orbit resistance and air resistance are applied on the rocket sled, greater water brake force is further applied on the rocket sled, and the greater heading negative direction acceleration is generated, such that the speed of the rocket sled body is reduced, the rocket sled body is safely recovered, the basis is provided for validation of the large dynamic performance of the inertial measurement apparatus, test preparation time, test cost, human power and material resources are saved under the premise of unchanging of the test equipment, and effectiveness and coherence of the test are ensured.