Abstract: In order to solve the step temperature problem during test of thermocouple time constant, fuzzy control algorithm was used to feedback control the laser output power, a new parameter adaptive fuzzy proportion-integration-differentiation control algorithm was implemented and the hardware of closed-loop control system was analyzed. The experimental results show that, the time constant data of K-type thermocouple is 421.1ms. The algorithm can effectively shorten the balance time and enhance the anti-interference ability of the temperature control system. This research is helpful for the calibration research of thermocouples, and has certain engineering reference and application value.