The thermal distribution of objects can be transformed into the visual pictures by the infrared thermal imaging system and displayed on the monitor in grey level or pseudocolor, thus the temperature distribution of objects can be obtained. According to the thermal imaging principle of temperature measurement and the characteristics of infrared images, the pseudocolor coding of infrared images is studied in this paper. A new pseudocolor coding, automatic threshold method, is presented. This method was proved by TMS320C6202 and FPGA thermal imaging systems at room temperature. Experimental results show that gradations of infrared images can be discriminated and different temperature regions can be easily resolved by the method.