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Abstract: In this research sewage sludge was taken photographs frequently with a high speed infrared camera during its whole pyrolysis process which took place at 400℃ to identify its photographic characteristics. Digital image processing was performed with help of software Image Pro Plus (v6.3) to obtain the quantitative parameters describing morphological characteristics of these photographs； and then the correlations between these morphological parameters and the pyrolysis steps were investigated. It was found that the main area of sewage sludge photographs under investigation and the optical densities of R (red)，G (green) and B (blue) of these photographs regularly changed with its pyrolysis process and they were the two target parameters. The concerned area of photographs under investigation reduced from 52 000 pixel to 35 000 pixel from the beginning of the sewage sludge pyrolysis to the end； while the optical densities reduced from 160~180 to 70 in the same process with an obvious linear relationship to the mass loss during this process. The optical density was proved to be the more accurate parameter to describe the pyrolysis process also by the fact that the curve of averaged optical density of RGB with reaction time well satisfied DoseResp function under the investigation conditions. All of these results cast a light suggesting that image analysis provides an innovative method for sewage sludge pyrolysis characterization and could be potentially used for the process control.