Abstract: The round-trip horizontal drift observation is a new type of observation method studied and implemented in China. It can effectively improve the observation efficiency and economic benefits and is of great significance to overcome the defects of the conventional radiosonde observation and improve the quality of numerical prediction. In this paper, according to the characteristics of thermal and dynamic processes and their main influencing factors in the rising and horizontal drift stages of sounding, a theoretical model of the thermodynamics of a horizontal drift on a sounding system is established. The reliability of the theoretical model is further analyzed and verified by combining it with the actual observation test. Research results have important theoretical support and practical value for designing and improving the round-trip drift sounding system.