The invention provides a novel composite material battery box body structure optimization design method, and belongs to the field of composite material structure design. In order to guarantee the sideextrusion strength, a reinforcing rib with the section being hollow is placed in the box body to serve as a structural reinforcing piece. In order to improve the overall rigidity and resist deformation, outward convex reinforcing structures are arranged along the four walls of the box body. In order to improve the rigidity of the bottom and ensure the pressure resistance of the bottom, net-shapedcrossed reinforcing ribs are arranged at the bottom of the box body. In regards to material selection, on the premise of weight reduction, a carbon fiber prepreg and a glass fiber prepreg are selected to carry out the overall laying design on the premise of reducing the weight. The weight of an upper cover of the battery box is reduced. The total thickness of the upper cover is H. In order to reduce the weight, the middle 1/3H material layer is replaced by the net-shaped crossed frame, and the basic rigidity of the upper cover is guaranteed. The mechanical simulation test is carried out, andthe pits are filled with a light material at the extrusion position of the side pressure head in order to better perform side pressure, so that it is guaranteed that the side pressure is evenly distributed during side pressure, and the rigidity of the side surface is improved at the same time.