Abstract: A new method for fine registration of a low-coherent SAR images pair in PS InSAR is presented and implemented. This method completes original registration of the low-coherent SAR images pair with the help of the third image that has higher coherence with the master and slave image, and then calculate the coordination mapping function between them using weighted least square method to achieve quickly and efficiently high precise sub-pixel level registration of the low-coherent SAR images pair. A registration experiment with ERS-1/2 SAR images is carried out and the results show that the method can improve the interferogram quality, coherence, registration accuracy of control points and registration effect between the low-coherent SAR images pair. So the new registration method can to some extent solve the registration problem of the low-coherent SAR images pair..