Abstract: The formation configuration design of distributed spaceborne interferometric SAR(DSInSAR) is key issue of system design.It must be combined with the flow of work and function of system.Because of its features of multisatic,squint angle and spacial baseline,spaceborne(multisatic) InSAR system must be analysed by new signal processing and performance evaluating methods.New restrictions of formation configuration design also must be put forward.Improved interferometric signal processing and performance evaluating methods are researched.Based on these new methods,restrictions of destance between master satellite and assistant satellites(formation),spacial baseline vector are presented.Distance restriction is based on analysis of bistatic radar SNR and time series.Spacial baseline vector restriction is based on analysis of DEM precision.Spacial baseline decorrelation which influence the interferometric phase error and DEM precision is analysed in detail.The quantitative and qualitative relation of spacial baseline vector,spacial(baseline) decorrelation,the intrferometric phase error and DEM precision is presented.Because(interferometric) Cartwheel and Pendulum formation is put forward based on side-glance geometry,simulation results show that the DEM performance of them are not optimal.