Aiming at the problem of blind despreading of short-code BPSK/DSSS signals under non-cooperative and low signal-to-noise-ratio(SNR) circumstances,an algorithm which hierarchically deals with the signal is proposed.Firsly the sequence′s spreading period are estimated. Then the initial bit of a short-code sequence is figured out by employing the auto-correlation properties of short-code DSSS signals.Two windows whose length is spreading period are constructed at the same time,and by inner products of the two windows the relative polarities of all the adjacent information bits can be estimated.The robustness of the proposed algorithm is improved by correction of short-code sequence′s initial bits via a sliding method in every iteration. Simulation results show that a BER lower than 0.000 2 could be achieved under a SNR above -2 dB,which proves the engineering application value of the propsed algorithm.