The present invention relates to a trench cross-section reference line setting device, comprising: a trench reference line setting body unit (100) for setting a trench cross-section reference line, wherein the trench reference line setting body unit (100) has a sensor unit (10) at the center thereof, two horizontal units (20) orthogonal to each other on the upper surface thereof, and three laser light source units (30) and a grid photographing unit (110′), respectively, on the side surfaces thereof; a reference line setting tripod unit (200) rotatably coupled to the trench reference line setting body unit (100) and having a posture adjusting unit (230) and a height adjusting unit (250); and a trench stratum analysis server (300) for receiving a fault image photographed by the grid photographing unit (110′) of the trench reference line setting body unit (100) and creating a stratum map of a trench cross-section structure.