Based on the accumulation of lock-in error, a method for eliminating the dynamic lock-in error by injecting multi-cycles step noise with white noise into the mechanically dithered ring laser gyroscope (RLG) is presented. The theoretical analysis proves that the multi-cycles step noise enhances the bias stability of RLG, as well as some intensity of the Gaussian white noise can reduce the accumulation of lock-in error during the step periods. The simulation experiment results show that this approach is prior to the traditional method in this way. Both methods decrease the bias error to the same orders of magnitude, while the bias stability is improved two or four times by injecting the multi-cycles step noise with white noise.