The invention provides a slope water flow depth calculation system, which comprises a digital terrain acquisition and processing system, a slope building system, an artificial rainfall system and a geographic information processing system, and is characterized in that the digital terrain acquisition and processing system comprises a camera array and a synchronizer; the synchronizer controls cameras in the camera array to shoot terrain images synchronously, the terrain images are analyzed based on a close-range photogrammetry principle and an oblique photogrammetry principle, and digital elevation models of a slope model are generated; and the geographic information processing system analyzes each digital elevation model and calculates slope water flow depth data of each grid. Therefore, the slope water flow depth calculation system provided by the invention can perform omnidirectional observation on slope sheet flow through acquiring the slope terrain data in real time and building the digital elevation models of the slope model, and can calculate the slope water flow depth on the whole slope in real time.