By using the correlativity between image gray value and temperature, the temperature that is hard to measure can be accurately obtained in some fields. The correlativity analysis between image gray value and temperature was proposed based on infrared target(IT). Self-developing infrared target was taken as a research object, which was a method to collect the infrared images which were taken at different temperatures (60-110 ℃) by infrared target with circular apertures. Matlab was used to extract the infrared image gray values (IIGV) of certain regions at different temperatures, which could ensure the correlativity between infrared target image gray value(ITIGV)and its temperature. The correlation coefficient of 0.962 was obtained. Experimental results reveal a good linear correlation between the average gray value of area of interest (AOI) in the infrared target images and temperature. With the change of infrared target temperature, infrared image gray values has changed. Both of them show a good linear correlation. The correlativity between image gray value and temperature based on infrared target has an outstanding effect on straw self-ignition in paper mill, medical security, road construction, etc.