The invention discloses a lower box body of a power battery and a manufacturing method thereof. The container is an open container integrally formed by a metal frame and a composite material completely wrapping the outer side of the metal frame. The metal frame is a rod assembly with a hollow area, the breadth of the metal frame covering the whole lower box body; the composite material is a wall plate formed by stacking more than one layer of fiber sheets and infiltrating and curing the fiber sheets in resin, and the heat conductivity coefficient of the wall plate is less than 1W/m*K. The preparation method comprises the following steps of: paving the composite material before and after the metal frame is embedded for several times; and pouring resin and curing resin into a whole. The lower box body with the optimized structure and the manufacturing method of the lower box body are applied to the power battery; the lower box body is integrally combined and formed by a polymer compositematerial and metal; compared with a lower box body purely made of a composite material or a metal material, the weight of the lower box body is reduced by 20%, meanwhile, the strength of the lower box body meets the requirements of GB/T31467.3, and tests show that the heat preservation time of the lower box body is prolonged by more than one time compared with a pure metal box body under the sameuse condition.