In this paper we analysis the performance of Rife algorithm and point out when the true frequency is much close to quantized frequency of DFT (discrete Fourier transform) Newton’s iteration will be disconvergent because of decreasing of Rife algorithm’s precision.In order to solve the problem we present a modified Rife (MRife) algorithm by moving the signal frequency to the midpoint of two neighboring discrete frequencies and then estimate the frequency using the Rife algorithm.The simulation results show that the performance of MRife does not fluctuate with the distribution of signal frequency.The RMSE (root mean square error) of one iteration of Newton’s method whose initialization is MRife is close to CRLB (Cramer-Rao Lower Bound) throughout the frequency band and the performance is steady.