A method for determining integration initial value of PID controller is applied to obtain an integration initial value for temperature control and to fast eliminate stability error. This method uses a set temperature value and temperature error setting to perform on-off switching with the range of temperature error setting after an automatic tune is activated. An amplitude for the highest and the lowest temperature curve is obtained. An integration is calculated based on the amplitude, the temperature value and the lowest temperature to obtain an estimated control initiation value for PID controller performing temperature. A stabilizing integration value is added when temperature is near a preset value to reduce temperature reaction time. Therefore, the dilemma of temperature overshoot caused by fast reaction and low reaction to prevent temperature overshoot can be solved.