Abstract: This paper first briefly describes the principle of BPSK (Binary Phase Shift Keying) modulation and BOC (Binary Offset Carrier) modulation. It then presents the analyses of the ranging precisions, the performance of tracking, and the multipath errors in using the two modulation methods. These are based on the real conditions of the Chinese Area Positioning System (CAPS), which was initiated by the Chinese Academy of Sciences. The results of our analyses can serve as guidance and have reference values in designing signal systems and choosing modulation methods.