Abstract: The stability of superluminescent diode(SLD) characteristics in the temperature of -45-70℃ directly affects the performance of fiber optic gyroscope, therefore, the stability of the constant current mode in the temperature of -45 -70 ℃ has become one of the key issues of system design and optimization. In this paper, the circuit model was presented and the analytic form of the temperature stability of constant-current source was given, and some design rules were also presented according to the formula. Meanwhile, using the analytical formula, the theoretical analysis and calculation of the temperature stability of the constant current source under several different conditions were done, consistent with theoretical calculations and experimental results. The performance of SLD constant current source can be effectively assessed with this formula, and it is of important guiding significance for the SLD driver design.