Security issues of the physical layer in wireless communications have attracted extensive attention in recent years. Meanwhile, the key space and encryption mechanisms have great impact on the security performance. This paper proposes a novel physical layer encryption scheme based on multi-fold chaotic maps in orthogonal frequency-division multiplexing(OFDM) systems. High security is achieved by performing the chaotic maps on the phase and amplitude of quadrature amplitude modulation(QAM) symbols, and the transmitted subcarrier. The initial conditions of the chaotic maps serve as the secret keys. Mathematical analysis indicates that the proposed scheme can provide a huge key space of 1.5 × 10 ⁹⁸ , which is much larger than that of the existing solutions. In addition, the transmission performance is evaluated over both AWGN channels and Rayleigh fading channels. The theoretical analysis and simulation results reveal that the proposed scheme significantly outperforms the existing solutions in terms of security. Meanwhile, it can achieve similar transmission performance over different channels.