A novel high-precision phase retrieval imaging method based on beam splitting amplitude modulation is proposed. The incident beam to be measured is split into many diffracted replicas by a two dimensional grating, and these diffracted beams are illuminated on a modulation plate with known structure. When the modulation plate is weakly scattered, the diffraction patterns formed on the detector are clearly separated with each other. Both the amplitude and phase of incident beam can be reconstructed iteratively by using the recorded diffraction patterns and the known structure of the modulation plate. This method has the high imaging speed of Gergberg-Saxton algorithm and the high precision of ptychographical iterative engine and potentially can be applied for X-ray imaging and online detection of high power laser.