An evaluation method based on image gray correlation algorithmic was put forward. The infrared camouflage probability was defined as an impersonal evaluation index to weigh the infrared camouflage effect through the correlation processing of the thermal images with or without camouflage measure and extracting characteristic parameters of correlation peak including peak notable degree,peak to correlation energy ratio and peak-to-background ratio. The statistic weights of different characteristic parameters were educed from the statistic results of human eyes distinguishing thermal images. So the computer image processing results can be consistent with the practical human eyes subjective distinguishing results. The experiment results show that the method is effective on evaluating the infrared camouflage effects of representative land military object.