Abstract: Focusing on the ambiguity problem of frequency offset estimation in DSSS signal synchronization, this paper presents a double acquisition algorithm of large frequency offset. This algorithm includes three steps. Firstly, pre-estimation and compensation of frequency offset is implemented by searching time-frequency domain in parallel. Secondly, frequency estimation points are constructed according to the result of pre-estimation and compensation. Thirdly, the frequency ambiguous of the signal is eliminated by double acquisition after frequency compensation. Finally, the correct signal can be obtained after the process in large frequency offset environment. Simulation and real test results show that the acquisition algorithm, which combines the techniques of large frequency offset pre-estimation based on the time-frequency search and fine frequency offset estimation based on FFT and double capture, can effectively shorten the time of DSSS acquisition and improve the acquisition probability in low SNR. The algorithm can be employed in DSSS receiver to satisfy the requirements of simple, flexible and high accuracy.