Abstract: Autonomous formation flying of multiple vehicles is a key technology for both deep space and orbital applications that involve multiple spacecraft. Many future space applications will benefit from using formation flying technologies to perform distributed observations （e.g., Synthetic Aperture Radar, SAR）. One of the key requirements of distributed SAR is accurate post-progressing knowledge of the relative positions between the vehicles. In order to realize the high-precision intersatellite relative positioning of the distributed SAR, an augmented relative positioning method based on the single-frequency GPS is proposed in this paper. With this method inter-satellite pseudorange measurements based on single-frequency GPS measurements incluing P-code and carrier phase measurements are added, then a spline model of relative positioning based on the continuity of the relative position parameters can be found and, finally the least-square method is used to estimate the parameters. The results of simulation show that this method can not only improve relative positioning precision greatly, but also reduce the epochs needed by fixing the ambiguity. The theoretical analyse proves the correctness of the results of simulations.