This paper analyzes the complexity and variability of actual underwater environments and discusses the impact of underwater absorption and scattering effects on underwater wireless visible light communication. To address the issue of channel variability, flexible modulation techniques are designed to adjust modulation rates and formats, enhancing the flexibility and applicability of the communication system. Additionally, based on time-division multiplexing, a time-division duplex control protocol is proposed, which realizes end-to-end adaptive modulation control through communication protocols. A set of adaptive control strategies is designed based on real-time communication status, integrating flexible modulation techniques with control protocols to achieve adaptive modulation for underwater wireless optical communication. Experimental results show that this technology can switch modulation modes under different attenuation conditions and maintain stable communication, thereby enhancing the reliability and flexibility of the communication system. It provides a high-speed, highly reliable communication method for underwater unmanned systems.