Differential interferometry synthetic aperture radar(D-InSAR) is further development of InSAR,and four-pass D-InSAR is one type of data processing by this method.Because many uncertain factors affect the accuracy of data processing of four-pass D-InSAR,it is not applied widely in the monitoring of land deformation.However,four-pass D-InSAR does not require an external digital elevation model and has the advantage of a possible guarantee of the accuracy of monitoring deformation.The baseline,visual angle, baseline tilt angle,slope range,satellite orbit height,ground resolution,and other satellite imaging factors significantly affect the capability and accuracy of D-InSAR measurement in monitoring land subsidence;satellite orbit error is the main factor affecting the accuracy of deformation measurement when using four-pass D-InSAR.The difference in satellite orbit and radar frequency is generated by various sensors of satellites acquiring radar images,which could also significantly affect deformation measurement with this method.The system and speckle noise,loss of pixel registration,visual number,and temporal and baseline decorrelation are the main sources of phase measurement error and significantly affect each pixel of images from the coherent radar,for which the phase error affecting the accuracy of deformation measurement when using four-pass D-InSAR is created.The baseline is generated by two different satellite orbits,which causes the baseline error to be systematic;hence,the baseline length error is also systematic.The baseline tilt angle affecting high altitude onboard the satellite is created by various uncertainties of the satellite and changes in baseline length.Consequently,the baseline tilt angle error has an effect on four-pass D-InSAR.The uncertainty of slant range is determined by the delay of the troposphere and ionosphere to the space-borne SAR satellite radio transmission,sampling clock jitter,and uncertainties of timing system of the SAR satellite,for which the interference phase of the InSAR diagram from four-pass D-InSAR is unstable.The uncertainty of terrain factors is generated by variation from the ground flatness,high and low topography,and vegetation coverage in the study area,which prevents the coherent radar images from effectively containing deformation information of target objects;thus,the influence on four-pass D-InSAR is apparent through the terrain factor error.An effective quantitative formula of phase on deformation measurement accuracy of four-pass D-InSAR is presented in this paper on the basis of the basic principle and data processing flow of four-pass D-InSAR.In addition,the effects of baseline length,baseline tilt angle,satellite orbit height,slope range,and terrain factors on deformation measurement accuracy of four-pass D-InSAR are analyzed and discussed.Finally,conclusions of the effects of errors on deformation measurement accuracy when using four-pass D-InSAR are drawn by the quantitative analysis.