Abstract: The staring observation of a certain region for geosynchronous orbit synthetic aperture radar (GEO SAR) is very important application. Due to the big SAR echo range migration in staring imaging which makes the signal reception window be difficult to choose, a pulse repetition frequency (PRF) variation method for geosynchronous orbit staring imaging is put forward. Firstly, the design criterion of pulse repetition frequency variation is given, and then both of the location of the missing pulse and the influence on imaging quality owing to pulse repetition frequency (PRF) variation are deduced in detail. The back projection (BP) algorithm is adapted to non-uniform sampling signal imaging focusing. Finally, the simulation is used to verify the effectiveness of the PRF variation. Numerical simulations have demonstrated the effectiveness of the approach proposed.