This paper investigates the synchronization of digitalized DSSS receiver in high-dynamic and Extra-low SNR environment, presents and realizes the methods of direct P-code acquisition in GPS. This paper introduces several conventional code acquisition methods and the reason why they are not fit for direct P-code acquisition. In the precondition of good cross correlation and partial autocorrelation of P-code, a direct P-code acquisition scheme based on Unsymmetrical FFT is proposed and realized in FPGA. Compared with the conventional slipping correlation method, the time of direct P-code acquisition scheme based on Unsymmetrical FFT is reduced by more than ten times and the calculation is reduced rapidly. It's useful for other direct long PRN codes acquisition.