In consideration of the importance of reference phase compensation to repeat orbit SAR interferometry and the significance of the reference phase to parameter selection and baseline reestimation in InSAR processing, the effect of reference surface difference that caused reference phase change is studied as well as the method of baseline reestimation. This paper gives out the analytical form of the reference phase and reference phase frequency in different reference surface, studies the difference of the reference phase and reference phase frequency characteristic and at last analyses the possible methods in baseline reestimation using reference phase characteristic. The paper also setup the theoretic basis for baseline reestimation based on reference phase characteristic. The study shows that the baseline reestimation could be achieved by utilizing the characteristics of reference phase, and the proper surface of reference phase must be selected since different surface of reference phase will cause different reference phase.