Abstract: High precision digital PID control system used in temperature control of electron beam brazing joint was realized.In order to keep the predefined joint temperature during brazing process, digital control model and controller were constructed based on computer control and discrete control theories.The type of the controlled object was determined by open-loop and closed-loop step responses, and the effect of the expanded ultimate-sensitivity method and the expanded step-response method were compared when the PID parameters were tuning.The PID parameters obtained by the ultimate-sensitivity method were optimized by the through normalization on line, and each group of parameters and the corresponding experimental results were provided.Integration separation algorithm was also used to enhance the dynamic performances.The experimental results show that overshoot is so small that can be ignored and time is not needed to adjust;the temperature control precision can reach ±2.5℃.