We report a low-complexity and high-security orthogonal chirp division multiplexing (OCDM) transmission scheme based on generative adversarial networks (GAN) enhanced chaotic encryption. Our investigation focuses on the security and efficiency of the communication system. To successfully apply GAN for the encryption scheme, we design our networks with new network architectures and modify the loss functions to improve the adversarial training performance of the networks. In the experiment, a weakly coupled seven cores fiber of 2 km was applied to achieve a 70 Gb/s transmission system. The results reveal that our proposed scheme has a maximum receiver sensitivity gain of about 1.26dB than traditional OFDM transmission system, and our encryption scheme has a large keyspace at about 1 × 10202 against brute force cracking by illegal optical network units with only 0.63% running time compared with the traditional chaotic scheme. The results highlight that the proposed encryption scheme has a remarkable reduction in complexity and improvement in security, which is a promising candidate for next-generation PONs.