The spectral radiation characteristic of a non-luminous flame is analyzed. The apparatus and the calibration procedure based on infrared emission spectrometry for measurements of the flame are introduced. The influence of background radiation and stray light on the measurement results could be reduced and suppressed by the design of thermolator and digital lock-in technique. A blackbody cavity was used as reference emission source to calibrate the system that completed absolute measurement. The spectral measurement range is 1---20 μm. The least measuring distance and the lowest power detected at the entrance pupil are 550 mm and 10^(-9) W/cm2, respectively. The experimental results show that the measure error is less than 10%.