An improved iterative phase retrieval algorithm is put forward, which makes use of intensity information in several planes, and divides the retrieval process into two steps: profile retrieval and detail retrieval. First the input plane and other three far diffraction planes are needed to retrieve the profile of phase distribution, then the phase detail is available in a similar way. The phase distribution of any one dimensional optical field, including very complicated ones, can be successfully retrieved with this algorithm, and the accuracy of retrieval is greatly enhanced. This algorithm is also very robust. It has convergence independent on the initial phase, and high stability towards additive noise, which are both confirmed by simulations.