Abstract: Because the frequency estimate precision of Rife algorithm has a great deviation when the signal real frequency is near to the discrete frequency, but the frequency estimate precision can reach Cramer-Rao lower bound when the signal frequency is near to the midpoint of two neighboring discrete frequencies. An improved Rife(I-Rife) algorithm is presented by moving the signal frequency to the midpoint area of two neighboring discrete frequencies and then the frequency is estimated by Rife algorithm. The ill-judged probability of correctional frequency direction can decrease sharply after using improved criterion. The I-Rife algorithm holds on higher precision even when the SNR reaches to-13dB, but it need lower workload owing to using spectrum subdivision technique. The simulation results indicate that I-Rife algorithm not only has good frequency estimation precision, but also has a good stability in all frequency domains. Frequency estimation of sinusoid wave based on the I-Rife algorithm can be achieved in real-time. It can be implemented easily by the hardware.