An additive manufacturing method for a 3D object is provided and includes (a) providing a 3D digital model of the 3D object; (b) dividing the 3D digital model into repeat arrangement of at least one type of polyhedral 3D units and an X-Y plane is an acute angle or an obtuse angle; (c) cutting the 3D digital model along a Z-axis into a plurality of 2D slices; (d) defining a scanning path covering one of the 2D slices; (e) providing an energy beam to a material on a working plane along the scanning path to form a construction layer corresponding to the one of the 2D slices; and (f) repeating the steps (d) and (e) to build up the 3D object by adding a plurality of construction layers in sequence.