The invention relates to a die structure for an automobile metal plate punch piece and a punching method thereof, and provides a slant punching die structure of the automobile metal plate punch piece. The slant punching die structure of the automobile metal plate punch piece comprises a first sliding block mechanism (15) which moves horizontally and is provided with a punching concave die (8) and a second sliding block mechanism which moves aslant and is provided with a punching convex die (4). A material returning rod (10) is connected with the first sliding block mechanism through a limiting unit and a reset spring (9). When the material returning rod (10) makes contact with a stop dog (13), the reset spring (9) is pressed, the end portion of the material returning rod (10) moves outward and stretches out of waste material (19) pushed out of a hole cavity of the punching concave die (8). The punching method comprises the four stages that a die is opened, and the punch piece is placed; the die is closed, and punching is conducted; punching is finished, and the die is opened; the waste material is pushed out, and the punch die is taken out. According to the slant punching die structure of the automobile metal plate punch piece and the punching method thereof, the waste material of a slant punched hole is guaranteed to smoothly flow to a waste material sliding plate or a waste material groove, at the same time, the specific intensity of the die can be improved, the conveying condition of taking and placing the punch piece on a production line is improved, stable component positioning is guaranteed, the production takt is improved, and the production efficiency is improved.