In fixed-receiver bistatic SAR (synthetic aperture radar), the spaceborne SAR was used as the illuminator. The direct-path signal and the backscattering echo were sampled, synchronized and focused by the receiver. The geometry of fixed receiver bistatic SAR was introduced. After the direct-path signal was used as reference signal for range match filtering, the spatial variation of chirp rate, range cell migration and two-dimensional spectrum were analyzed. Based on azimuth preprocessing, direct-path signal compensation and nonlinear Chirp Scaling imaging algorithm, a new focusing algorithm was presented. Simulation results of point targets were presented to validate the feasibility and efficiency of the proposed method. This algorithm was also validated by the measured data of the HITCHHIKER system.