Abstract: The ocean is a strategic important for the national high-quality development, and marine monitoring is an important way to understand and develop the ocean. With the continuous implementation of Marine power strategy such as "One Belt And One Road", higher requirements are put forward for Marine surveying equipment. Therefore, using the combined GPS/BDS system and electronic compass to provide high-precision position and heading information, and equipped with monitoring devices, the new unmanned semi-submersible vehicle is applied to marine environmental monitoring. Aiming at the influence of uncertain model parameters and environmental disturbance on the reliability and stability of the heading monitoring of unmanned semi-submersible vehicle, an adaptive sliding mode control (ASMC) method was designed based on the strong robustness of sliding mode control (SMC) and the high adaptability of adaptive control. Theoretical analysis and simulation experiments show that the ASMC is feasible and effective, and has better adaptability and robustness than the traditional proportional plus denriva tive (PD) control, and the system has good transient performance and stability. The designed adaptive sliding mode control method is applied to actual marine monitoring, and the test results show that the control effect is stable, the surveying data is real and reliable, and the surveying efficiency is improved.