Abstract: Based on the analysis of characteristic of lattice beam and cable engineering,the internal force of lattice beam is computed by Winkler elastic foundation beam theory,the method of assign load in the decussating node is discussed to overcome the disadvantages of present method,and the formula of internal force of the beam with finite distance is conducted.The space,section dimension and cantilever length are discussed via a project to guide optimization design.The results show that the design of lattice beam ought to use small space,less section dimension and the lattice beam should have appropriate cantilever length.