Abstract: The paper presents the structure and the working principle of a humidity control system for the satellite service module. The mathematical model of the system based on the transfer function is constructed by combining the analysis and the measurement. The accuracy of the model is verified by the test, and the system characteristics are analyzed in terms of the model. The analysis results show that the system can meet the technological requirements. Further possible improvements of the system characteristics are outlined, which provides a basis for improving the design of the system.