With the wide application of OFDM technology, the security of OFDM system is becoming more and more important. In this paper, we propose a secrecy transmission scheme with phase rotation and sub-carrier mapping based on chaos sequences. The scheme employs the characteristics of pseudorandom and sensitivity to initial conditions of chaos sequences. We have studied on the observed signal features, computational complexity and possible key number, as well as error-correcting performance of proposed scheme. It's shown by simulation results and analysis that the scheme is able to effectively encrypt the information and enhance the randomness of output signals. The malicious receiver cannot estimate the message through the statistic characteristics of received signals, which ensure the aim of secure communication.