I-V temperature characteristic is very important to InSb IRFPA. In order to make further studies on I-V temperature characteristic, some experiments were done. In the experiments, the operating temperature of the InSb array was gradually raised from 77k. It is shown that reverse current doesn't simply increase with the increase of the operating temperature. The reason can be attributed to the composing of reverse currents at different operating temperature. In this paper, the I-V characteristic of InSb diode at different operating temperature is briefly described. The dominant components of reverse current and its temperature characteristic are discussed. The change of detector impedance is analyzed as operating temperature is changed. At the same time, the optimized operating temperature of InSb IRFPA is presented. The limit of operating temperature at which InSb IRFPA can work normally is also given.