A sensor head design scheme by adding a heat-off spool to the fiber coil is studied to improve the Fiber Optic Current Sensor (FOCT) temperature performance which is vital to the precision of FOCT. The discretized mathematical model of the output error of the FOCT system is deduced and established based on the thermal phase difference caused by the temperature disturbance of the fiber coil. Then, the finite element model of the fiber coil itself and the fiber coil with the heat-off spool is established respectively by using the finite element analysis software, and the thermal performance of the heat-off spool and the temperature performance of the FOCT with new sensor head under different temperature loading schemes are simulated and analyzed. Simulation results show that the heat-off spool actually can control the temperature change range of each fiber in the fiber coil, slow down the temperature change rate of the fiber, equalize the temperature field of the fiber coil. Besides, the output error range of FOCT system with the proposed sensor head is obviously reduced, and the system measurement accuracy be improved effectively, which is important for the high-precision FOCT′s production and application.