Abstract: To lower the influence of optical source temperature property on the precision of fiber optic current sensor(FOCS) in high voltage grid, an analog temperature control system was proposed to control the optical source working temperature. According to the designed goal, design process of each key section was introduced. A proper temperature signal bridge was analyzed which could obtain a linear relationship between the output differential voltage and temperature. The mathematical model of the system was established in the frequency domain; the transfer function of the system was calculated; and the parameters of proportional-integral-derivative (PID) controller were analyzed in the time domain. A temperature controller used for FOCS super luminescent diode (SLD) optical source was designed, which was verified by fixed temperature test and temperature cycle test. The results show that by means of the real time temperature control, the accuracy of FOCS is up to 0.2 level which reaches industry requirements.