Abstract: The development of nanosatellites in recent years poses new challenges for the thermal control system with respect to the rapid iterative design and the low-cost manufacturing. This paper first assesses the technical requirements and the difficulties in the design of the nanosatellite thermal control systems. The calculation method for the external heat flux on the spacecraft on the common elliptical Earth orbits is proposed, as well as the method of the continuous integration of the spacecraft thermal balance equation and a simplified method for analyzing the lumped node-based temperature field, with consideration of the particular structural and heat transfer characteristics of the nanosatellites. A mathematical model based on these methods is built and implemented for a nanosatellite example, and the results are validated with the Thermal Desktop software. It is shown that compared with the tedious meshing and time-consuming calculation procedures in the conventional practice, our method can promptly model and determine the temperature in the main components on a nanosatellite. This paper provides an efficient evaluation tool for the early-stage design and the optimization of the thermal control system for nanosatellites.