The invention discloses a three-dimensional scanning device based on a laser triangulation method and a scanning method. The three-dimensional scanning device based on the laser triangulation method comprises a supporting base, a material turning assembly, a mechanical arm and a scanning assembly, wherein the material turning assembly and the mechanical arm are installed on the upper portion of the supporting base, the scanning assembly is installed at the output end of the mechanical arm, the material turning assembly comprises two supporting columns, a material turning motor, a supporting frame and a material fixing part, and the scanning assembly comprises a connecting piece, a camera and a laser. According to the invention, a to-be-detected mold is placed on the inner side of the supporting frame, a material fixing piece is operated, the to-be-detected mold is fixed on the inner side of the material fixing piece, the camera and the laser are operated, and the mechanical arm is operated at the same time, the mechanical arm drives the camera and the laser to move on six axes, the upper side of the mold is comprehensively scanned, the material turning motor is operated, the material turning motor operates to drive the transmission shaft to rotate, and then the supporting frame is driven to rotate, so that the to-be-detected mold is turned over, and the lower side of the mold can be scanned.