Considering the problem of engineering geological logging technique by means of sketching at the work site, this paper presents a photographic geological logging technique based on photogrammetry as well as engineering geology. The principles, methods, and working process have been discussed, and the photographic geological logging precision of a tunnel and its estimation method have been researched. The theoretical and experimental analysis shows that the precision of the digital unfolded image map of tunnel automatically generated by the photographic geological logging method is sufficient for serving as the logging base map. Besides, the measurement precision of unfolded images or stereopairs meets the requirements of geological attitude measurement. The new technique of photographic geological logging proposed in this paper is expected to replace the current sketch way of engineering geological logging on site, with the operation mode converted from manual operation to computer-aided operation and informatized management.