In the single-beam illuminating 3PIE (ptychographic iterative engine) method, the specimen is vertically illuminated without considering the influence of oblique illumination on the reconstruction result. In this paper, a dual-beam illuminating 3PIE method is proposed on the basis of the single-beam illuminating 3PIE method, and the simulation result shows that the reconstructed images are influenced by the phase inclination factor of the initial guessed illumination light beam. In the process of iterative recovery by the proposed method, two light beams are used to update the complex amplitude distribution of the same specimen area. The proposed method is demonstrated theoretically and experimentally. The results verify that the method can improve the convergence speed while weakening crosstalk between different specimen slices, and it is suitable for three-dimensional depth resolved imaging.