A real-time detection system of billet surface temperature measurement in furnace was designed, employing DSP as the image processing center. Two near-infrared radiation images were collected in the furnace, and the billet surface temperature was calculated using the colorimetric thermometry algorithm. The principle of colorimetric thermometry, the system hardware, software and testing effect are analyzed. The testing in the H-beam furnace show that the system can check the whole surface temperature of billet real-time, display the temperature field using pseudo-color image, and analysis the operating conditions of furnace. The relative error of temperature detection accuracy is less than 0.5%, satisfying the demand of the furnace control system.