Abstract: The rapid development of FPGA and its powerful parallel processing ability make it play more and more important role in SAR signal processing and some other high speed real time signal processing areas. This paper takes a spaceborne SAR signal storage and pretreatment system based on FPGA as an illustration, with modularization method, FPGA effectively realize the function of managing and controlling multichannel 2GB SAR signal memory, FIR filtering and downsampling. Of these modules, this paper emphasizes design and implementation of threeport SDRAM controller module and filtering and downsampling module.