In this paper, we suggest blind source separation (BSS) technology for primary users detect, which is very important in cognitive radio (CR). Multiple-antenna system should be a part of CR. Different antenna receives the same CR signal from different path, if only CR is being working. When primary user starts working, different antenna receives mixed signals of CR and primary user from different path; which can satisfy the BSS situation. CR can separate different signals with little collision. At the next time, CR can jump to next carrywave or modulation type.