The thermal imager based on uncooled infrared focal plane technologyis widely used in the field of noncontact temperature measurement with its low price and small size. The current thermal imagers can detect different temperaturebut it hard to obtain the specific temperature of the targets. Besides, the thermal imagerswhich has completely packaged is expensive and hard to redevelop. Based on these problems, a thermal imaging system was built based on FPGA and MATLAB,a method to obtain the temperature detection algorithm was provided in this paper. This method can obtain the electrical signal to specific temperature algorithm and its key coefficient. The experimental results show the error of the temperature algorithm is so small that it has a strong engineering significance for temperature detection warning systems.