In order to use the frequency resources rationally and effectively and not interfere with each other in a limited band of satellite navigation and positioning system, the direct spread-spectrum signal acquisition based on BOC modulation method was used. An improved single side band (SSB) average method was proposed for the traditional SSB processing method and its performance was analyzed. The simulation results show that SSB average method can effectively reduce the noise, and more significant result can be obtained. Compared with conventional SSB processing method, the improved algorithm can greatly reduce the acquisition time, reduce the error rate, and the capture accuracy is improved greatly. It is a fast and effective BOC modulation acquisition algorithm.