In order to solve the problem of rapidly acquisition for weak signal in the Global Position System (GPS), a new improved weak signal acquisition algorithm is proposed which improves the past coherent and incoherent integral gain based on Fast Fourier Transform (FFT). The proposed method uses batch mode to improve capture gain adopting doppler compensation and improves signal accumulate time tolerance, and the method can further improve the signal capture sensitivity. Comparing with traditional algorithm the capture probability rises greatly and it has been proved fully by lots of simulation tests. Finally the method is implemented on FPGA.