The influence of the frequency for the high frequency voltage signal made on estimator was studied when the initial position was estimated with the theory of highfrequency voltage injection was employed. The theory of highfrequency voltage injection was introduced to estimate the initial rotor position of PMSM. Meet the minimum injection frequency estimation convergence was deduced. The influence of injection frequency on the estimate accuracy and speed of the rotor position observer was studied theoretically and experimentally, thereby suitable range of injection frequency was developed. Experimental results indicated that the reasonable cutoff frequency and appropriate injection frequency could effectively balance the estimating speed and precision of the estimator.