The integral time adjustment is the primary means to extend the dynamic range of the infrared radiation measuring system. A real-time integral time adjustment method based on radiation calibration was put forward according to the radiation dramatic changes for the re-entry high-speed target, tracking affection and image saturation when integral time is adjusted. Radiation calibration can get the response and the bias of different integral time; the target radiance and the background radiance at the entrance pupil can be calculated by the target information and the background information. Then, the target's and the background's signal value on the other integral time can be computed by the target radiance and the background radiance. The optimal integral time can be predicted by the tracking criterion. Experimental results show that the method can accurately locate the optimal integral time, reduce the number of integral time adjustment in the measurement process, and realize the target continuous tracking accuracy rate of 100%.