We propose a method to estimate the InSAR(Interferometric Synthetic Aperture Radar) interferometric phase based on the model of joint single pixel.In the method we construct the optimal weighted data vector by different coregistration error size and direction.The method takes advantage of the coherence information of neighboring pixel pairs.Therefore it can auto-coregister the SAR images and reduce the interferometric phase noise simultaneously.Theoretical analysis and computer simulation results show that the method can provide accurate estimate of the terrain interferometric phase (interferogram) even if the coregistration error reaches one pixel.