The satellites SAR system is an imaging technology that has been paid much attention recently, one of the examples is InSAR system, which provide 3D image by interferential height measurement based on the formation flying satellites＇ baselines. In formation flight InSAR system, the configuration of satellites＇ constellation should be carefully designed to achieve a high precision and good quality. In this paper, the influence of height measurement accuracy that caused by satellites relative motion is studied with analysis on measurement precision of the height and flight dynamics. Two types of baseline directions were discussed in particular. One type is ＂vertical baseline＂ and the other is ＂horizontal baseline＂. On the basis of analysis, the concept of ＂preponderant arc＂ is put forward. The analysis can be used to determine the satellites＇ formation. Utilizing Hill~equation, the expressions of how the length, azimuth angle and pitch angle transformed with time were given. Finally, a new constellation configuration different from current system based on the analysis results is proposed. This formation includes three satellites, two satellites run concomitantly in a vertical plane, and the other runs in a sidelong plane. Some basic analyses for the performance are also presented. The simulation shows that this formation is feasible.