In this paper, a novel sensorless control strategy is proposed to solve the problem of sampling delay in the traditional square-wave signal injection method. A square-wave voltage vector is injected in the estimated rotating reference frame. Then, Fourier decomposition and discretization are used to analyze the values of the currents in estimated d- and q-axis, and the rotor position error is obtained through the calculation of the discrete currents. The influence of the sampling delay is reduced. Meanwhile, the effect of the amplitude and frequency of the injected signal is eliminated in the demodulation process. Compared with the conventional demodulation method, the proposed strategy shows a better stability and dynamic property. Finally, experiments are carried out to verify the correctness and effectiveness of the proposed method.