To get infrared radiance characteristics of a target while it was tracked, a radiance calibration system for infrared focal plane arrays (IFPA) was design. By taking a high-accuracy plane blackbody as a standard source, a mid-wave camera whose spectral response range is 3 μm to 5 μm was calibrated. Firstly, the calibration methodology was established and calibration procedures were decided. Then, the linear regression model was used to fit and evaluate the goodness of response and a eliminating the outlier method was taken to improve the fitting curve of the response. Finally, the target of known temperature and characteristics on the spot was measured in a field,and the actual observed value of infrared radiance characterization was obtained by fitting response curve and atmosphere transmittance. Calculation indicates that relative errors of the actual observed value to the theoretical value are less than 3%. The result confirms that proposed method can improve the uncertainty caused by the nonlinear of IFPA response.