Abstract: With the rapid development of wireless and cognitive network technology, the security of wireless communication has faced great challenge, in which parameters of wireless communication such as modulation type and frequency are more likely to be detected. As a result, business, especially military communication faces the problems of pertinence interference and content security, which are becoming more and more serious. In this study, a hiding algorithm for OFDM constellation mapping based on physical layer encryption is proposed. A secret seed key is adopted to control the phase rotation factor and amplitude size, thus the OFDM constellation mapping process based on MPSK/MQAM was disrupted. In this way, modulation modes used by legitimate users cannot be detected, thus modulation protection was achieved and illegal users cannot distinguish the modulation type. Simulation results show that this algorithm has a high capacity of modulation hiding on the premise of not changing the original system performance.