A combined method of high precision temperature control and its application in a constant temperature trough were presented. Combining Fuzzy logic with intelligent PID control of expert type, the method fully utilizes the expert's experience of manual manipulating and quantitative operating feature of PID control. Therefore, it could meet the precision and adjusting time requirements in high precision temperature control. Moreover, a novel and simple model to modify PID parameters and a method to predict the change of temperature on-line were introduced, which are easy to implement. When used in a constant temperature trough, the control accuracy of the combined method is even smaller than 0.01��.