The invention provides an onboard LiDAR data based dike damage detecting method aiming at actual requirements for dike tour inspection management. Through collecting dike onboard LiDAR data and through point cloud data filtering, high precision dike DEM data is generated for ground point cloud interpolations. On this basis, the high precision DEM is utilized for generating a dike slope map and a vectorization data product thereof. Pattern spot fusion operation is utilized for removing broken map spots, so that dike top and dike shape parameters are extracted. Through combination with dike linedata, an equidistant dike section is constructed. Through intersection of a dike section line and the dike top and the dike slope of the dike, an intersection point set is calculated. Dike damage detection on the section line can be realized through counting the number of the intersection point sets of the section line. The high precision DEM data generated by the onboard LiDAR can express groundshape change in a delicate manner. The method can detect dike damage efficiently and can be used for dike tour inspection management of a hydraulic engineering department, so that dike damage detection efficiency is improved substantially and good application value is achieved.