The invention discloses a slab bridge point cloud-based automatic component detection method and system. The method comprises the following steps of: aligning a bridge floor axle wire of a slab bridgewith a standard coordinate axis set in a global coordinate system through obtaining point cloud data of the slab bridge; and slicing different data sets, defining each slice by utilizing a bounding box, carrying out classification according to the height and size of each bounding box so as to finally recognize the components such as a bridge pier, a bridge floor and/or a pier cap. According to the method and system, the stage of generating surfaces from points is completely bypassed, and point cloud cut point sets with semantic tags are directly obtained.