A real-time IMU emulation method for GNC method includes the step of receiving real-time flight data from a 6DOF flight simulator and generating simulated IMU electronic signals according to the IMU measurement modules and error modules defined by the user, and injecting said simulated IMU electronic signals into an on-board GNC system which causes the on-board GNC system into "thinking" that the vehicle is really moving. The on-board GNC system which is installed on the vehicle is motionless during the emulation test, so that the testing can be carried out in a laboratory or in an anechoic chamber facility and the IMU emulation can achieve the easy, effective, and least intrusive injection of emulated IMU signals into the INS computer. The present invention has features supporting the final integration of a developmental Guidance, Navigation, or Control (GNC) system installed into a vehicle. It assures testers that GNC avionics on-board vehicle work properly before and during a flight test. It also helps to debug on-board GNC avionics and verify system performance.