Abstract: A fuzzy method for controlling the engine coolant temperature is prposed. The fuzzy rule base is correspondingly established based on the experimental data. The control query table is created through computing and analyzing via the fuzzy logic tools in MATLAB. The hardware system, centering on MC68HC908LJ12, is conducted. The software is designed as well. The test indicates that only a little improvement of the current engine cooling system can better solve the problem that it is difficult to accurately control the engine coolant temperature.