Objective: Based on clinical medicine information digitization and the construction and development of hospital informatization, the medical image information has realized the network archiving and communication and network diagnosis. Besides the performance of imaging equipments and the cognition ability of diagnosticians, the diagnosis environmental conditions affect similarly the imaging quality and the diagnosis effect directly during the process of digital radiation imaging. To start with environmental factors to review the difference in image reading effects under different ambient illumination. To expect to obtain the optimal illumination conditions. Methods: Medical image diagnosticians of different seniority are invited to participate in this study. Based on signal identification theory and receiver operating characteristic curve (ROC) analysis approach, we altered the ambient illumination of diagnosis environment to investigate separately the different observation effects on the same ROC pattern image under identical window width and window level. The detection capability of image details was reflected through the true positive rate and false positive rate of details detection. Results: The optimal illumination parameters were obtained. The luminance is approximately 0.63-3.18 cd/m2 in X-ray diagnosis film reading room. That is approximately 4.78-19.1 cd/m2 in CT/MR/NM film reading room. Conclusion: The analysis results show that the detection capability of image details fell down with the increase of the level of ambient illumination in routine medical image diagnosis environment.