Abstract: The influence of SAR system resolution to the image power spectrum density is represented. The one-dimensional circular power spectrum of SAR image is modeled based on negative exponent function and the relationship between the SNR of scene matching and the system resolution is deduced. The equations of SAR system resolution and independent pixel number are deduced from the autocorrelation function. The impact of SAR resolution to the independent number is analyzed in theory. Finally the relationship between SAR system parameters and acquisition probability is established. The simulation and experiment show that the model could describe the relationship among the SAR system resolution and the SNR of scene matching and the image independent pixel number very well. It provides the theoretical basis for the parameter design of scene matching trimble autopilot based on SAR.