There is strong coupling between environmental control system and thermal control system of manned spacecraft in terms of heat and material flow. In the design stage, it is necessary to carry out integrated system simulation analysis, so as to predict and verify the system performance. A typical integrated environmental control and thermal control system model of manned spacecraft is built using system modeling and simulation methods, including crew module, air purification module, air supply and pressure regulation module, fluid loop module, etc. The performance of the system is analyzed. The simulation analysis was carried out for the manned flight conditions of three persons in 7 days. The results show that the parameters of temperature, humidity, pressure and oxygen partial pressure in the cabin can be controlled within the requirements of aerospace medical indicators by reasonable design. The simulation results of the environmental control system and thermal control system accurately predict the working process of the system, show the changes of the main parameters, and the results are reasonable, which verify the correctness of the simulation method and the system simulation model. By controlling the opening of the bypass valve in the outer loop of the fluid circuit, the temperature of the control point in the outer loop can be accurately controlled to ensure that the temperature and humidity in the cabin are within a reasonable range. In addition, the setting of temperature control point in the outer loop will affect the state of the environmental control system and thermal control system. By reasonably designing the temperature control point in the outer loop, the temperature and humidity in the cabin can be guaranteed to meet the requirements of aerospace medical indicators. The research results play an important role in the integrated design and optimization of environmental control system and thermal control system.