The phase can be retrieved by the line integral of its gradient of horizontal and vertical directions, being calculated by the sine and cosine components, which are gained by Hilbert transform twice from a single carrier frequency interference fringe pattern. However, the result is not correct using the integral method when the gradient is discontinuous caused by fast phase change. Aiming at this problem, a two-dimensional optical field in the complex domain is built. By this way the principle of shearing interferometry is introduced to the digital phase retrieval to obtain a continuous phase gradient. The triple integral method is proposed to retrieve the original phase. Experimental results represent that the proposed method can solve the problems of phase discontinuity and fast phase change. The original phase can be retrieved more accurately.