This paper introduced an enhanced GPS software receiver which can rapidly process weak signals in challenging environments. In the traditional GPS receivers, the acquisition and tracking of the signals are usually processed by hardware devices, such as the Application Specific Integrated Circuits (ASIC). The main disadvantage of ASIC is the high cost of system reconstructions. While a GPS software receiver can perform almost all the operations in a programmable microprocessor, which makes the system more flexible. The specific software correlator inside can greatly accelerate the speed by the bit-wise parallel algorithm which changes large numbers of multiplications into exclusive-or operations. In the acquisition process, the block acquisition method was introduced here to solve the weak signal processing. In the tracking process, the Delay Locked Loop (DLL) and the Phase Locked Loop (PLL) were used for code tracking and carrier tracking respectively. The whole software was developed based on C language under Windows XP environment. Both the simulated GPS data and actual GPS signals were used to verify the performance of the acquisition and tracking processes. The simulation results showed that the software receiver can work properly in real time even in hostile environments.