To improve the accuracy of inertial navigation system (INS) during long time operation, the rotation modulation technology (RMT) was employed to modulate the errors of the inertial sensors into periodically varied signals in navigation frame, and, as a result, to suppress the divergence of INS errors. Firstly, the principle of single-axis RMT was expounded based on the measurement error model of inertial measurement unit (IMU). Then, the effects of vehicle angle motion upon RMT were analyzed theoretically. Error equation of equivalent gyroscopic bias in navigation frame was derived. Finally, the simulation and wobble tests were performed. The results show that the average effect of the RMT is negated by vehicle level angle motion; the more the angle amplitude and speed, the more inefficient of RMT, thus, the performance of INS is in low. It can serve as the reference for INS performance analysis and inertial sensors selection of single-rotating INS.