Abstract: Compared with other imaging algorithms for spotlight SAR， the polar format algorithm(PFA) prevails in some aspects， such as the lower range data rate and the compatibility with autofocus. However， it also has the demerits of computational burden and errors due to the two interpolations in both the range and azimuth wave number domain. In order to overcome the demerits above and improve the application of PFA in bistatic SAR， the Chirp-Z transformation has been introduced into it. The imaging procedure of bistatic SAR has been derived in detail. Then the efficiency in computation and precision of our method has been validated via both theory and simulations.