The segmented aperture optical system is widely used in the field of remote sensing for its advantages in reducing the manufacturing complexity to achieve high imaging resolution. However, the misalignments among these segments may result in phase errors, and degrade the imaging resolution of optical system. Phase diversity phase retrieval is adopted to resolve this issue, which solves the misalignment of segmented mirrors inversely and provides the basis for aligning on-orbit. The misaligned optical system mathematical model for segmented primary mirror is set up, and the difference between the model output and actual output at the known defocus is regarded as the target function of misaligned phase estimation. After being compared with other methods of resolving nonlinear equation, BFGS method is used to seek the optimum phase value. The result of the simulation experiment indicates that the method of phase diversity phase retrieval can control the phase error below 6%.