Abstract: A prototype of software global positioning system(GPS) receiver based on software defined radio techniques to design a flexible and reconfigurable receiver with a wide range of applications was discussed. Compared with hardware GPS receiver, there is a need for a unified platform that allows software receiver development and research for Ultra-Tightly coupled GPS/INS navigation system, speeds the design process and reduces the costs. A complete software GPS receiver was implemented using fast fourier transform(FFT) acquisition approach, delay locked loop, phase locked loop, and the receiver is able to perform acquisition, code and carrier tracking, navigation data decoding, pseudorange calculations, and position calculations. Compared with Novtel-s FlexPad hardware receiver, the results shows that software GPS receiver is effective in acquisition ,steady in tacking and it-s positioning error is less than 10 m,so it can be applied to an ultra-tightly coupled GPS/INS system.