In the thermal radiation measurement technology, the nonlinear effect of infrared detector leads to some error in target infrared radiation measurement. Based on blackbody radiation law, the thermal radiation curve of blackbody at different temperatures and certain wavelength and bandwidth is calculated theoretically. The thermal radiation measured by infrared detector is obtained experimentally with the same parameters. The detection curve of detector is modified by the theoretical curve. The nonlinear effect of detector is corrected, and the measurement accuracy of thermal radiation temperature measurement is improved.