IR can obtain the object information that is difficult to be obtained by the visible light. The infrared radiation characteristic is an important optical characterization,and it is widely used in target tracking and identification. A certain theodolite can be used as middle infrared target tracking device. According to the detection requirement of target infrared radiation characteristics,the infrared system of the theodolite needs to be modified. The composition and working theory of infrared radiation measurement system are analyzed. The infrared system of the theodolite is designed from several aspects including the temperature drift compensation,calibration equation acquisition and the dynamic range calculation of the camera,and the performances of the new system was tested. The results show that the design is reasonable,and can reach the expected goals.