One phase retrieval method based on the Talbot effect of Ronchi grating is proposed. A CCD camera is placed at the Talbot distance of Ronchi grating to record the self-image intensity distribution of Ronchi grating. By using the stochastic parallel gradient descent (SPGD) algorithm, the coefficients of Zernike polynomials are optimized to retrieve the input phase. The numerical simulation results show that, the proposed method can quickly achieve a high-precision phase retrieval and possesses the advantages of fast convergence, high precision, and anti-noise and so on.