Abstract: A new method for the geologic logging of digital photos of tunnels and its principle are introduced.This paper also discusses the basic algorithm of digital photo geologic logging for tunnels, i.e. digital image rectification, digital image mosaic, measurements of geologic elements of attitude of layers, and the generation of logging graphs.Practice proves that the project of geologic logging of digital photo based on a normal digital camera is quite effective.And the validity of the algorithm has been veritied.