Abstract: We propose a new method to solve the key issue of space decomposition for three-dimensional packing: Once loaded with a cargo, the box space is divided into an upper-space and an L-space. According to the space occupancy rate of the L-space, the L-space is divided into left-space and right-space. Thus the method can effectively reduce deformity space, which facilitates the subsequent loading of goods. Furthermore, we provide an improved ternary tree structure to express the decomposition of the upper-space, the left-space and the right-space. The experimental results show that the modified space decomposition method has a better loading effect compared with the conventional loading space decomposition method.