Abstract: In non-cooperative spread spectrum communication system, rapid acquisition of long period spreading code has been the key problem when signal-to-noise ratio (SNR) is low. To solve the problem, we propose a new rapid PN code acquision scheme based on multi-pass soft fast correlation attack. By regarding the PN sequence as a linear block code, the acquisition problem can be viewed as a decoding problem. To make full use of the soft information of the sequence, the decoding problem is achived through a soft decision method,and thus accomplished a fast acquisition of the long period code.Theoretical analysis and simulation results show that the performance of the proposed scheme is irrelevant to the number of the feedback taps. Our methods can work steadily when SNR is low. Compared with the multi-pass hard fast correlation attack, our algorithm has more than 3.5dB performance improvement.