Using high-accuracy extend blackbody as the standard radiation source, we set up the radiometric calibration system and perform a radiometric calibration experiment for long wave infrared camera. Based on the practical response data, the relationship of response characteristics with incident radiation and integration time is analyzed, and a mathematical model of radiometric calibration is establish. Thereout, the fast radiation calibration method, which is choose of three pictures under two temperatures at two typical integral time, is proposed. The unknown parameters in the calibration model can be obtained by data processing. Finally, using 398 sets of available data from 420 sets of measured data, we verify the reliability of the simplified radiation calibration model. The results show that the relative error between the calculated and measured values is less than 1%, and the fitting degree is greater than 0.999. Experiments show that the calibration method can ensure the accuracy of rapid radiation calibration under different integral time.