Abstract: Based on the structural characteristics of spacecraft propulsion sub-subsystem, the considerations in the thermal control of the subsystem are introduced. The problems focus on the thermal cycling fatigue of the diaphragm of the propellant tank, and the overheating of the valves with respect to the spacecraft of long service life. The general temperature control measures for both the active expulsion tank and the engine and thruster in the HT condition are expounded with discussion of the engineering difficulties. Then, an actual example is given with analytical predictions. Suggestions are made of the design of thermal control subsystem for long-life spacecrafts.