Abstract: The temperature control system of a blackbody in the vacuum cryogenic environment is a nonlinear and hysteretic system, and its mathematical model is not easy to build. Based on the analyses of the structure, components and the system in general, an algorithm of fuzzy control and intelligent PID control is developed for temperature adjusting of the system. A set of fuzzy control rules are established with sufficient digesting of the test data. The self-developed software, based on that algorithm, achieves auto-control and is used in some irradiation calibration tests. Test data validate the applicability of the control algorithm, which accelerates the warming up process, improves the system stability, and achieves a satisfactory temperature control.