By quantifying the gray scale on the location of carcinoma and the borderline of the fluorescence image, the fluorescence pixels and the true location of carcinoma were calibrated, and the quality of the fluorescence image of carcinoma was reflected objectively. The carcinoma fluorescence images were taken at different time. After nomalizing the images,their average gray scale and standard deviation were calculated to obtain the gray scale to extrac the borderline of carcinoma. It was shown that the strongest intensity of the animal modles with S180 sarcoma was found at 14 h after injecting the photosensitizer, while the best diagnosis accuracy was obtained at 18 h. This study could increase the feasibility of detecting carcinoma during the surgrey in real-time and giving important information for early stage carcinoma diagnosis.