A method for tracing pollution at a drainage outlet of a culvert. (1) The main line of the culvert is fully detected through an inspection robot to obtain the image data, water quality data, coordinates and other basic data of the outlet. (2) The type of the outlet is determined according to the data information obtained in step (1). (3) Pollutants in the drainage outlet with suspected rainwater-sewage connection are traced, and sources of the pollutants flowing to the outlet are all located.