The design process of structure optimization was discussed with an example of a diagonal square pyramid space grids simply supported at its perimeter. The grid structure height and member cross section dimensions of space truss were taken as the discrete variable variables.The total weight of space truss was considered as the objective function.The restrain condition such as strength,stability,stiffness and the structural deformation were considered.The one-dimensional search method and the modified stress ratio method are adopted as the optimization method and draw up optimization of the space truss structure making up with ANSYS Parameter Design Language(APDL).The calculated results showed that the weight of space truss reduced by 14.1%.Thus the optimum design can obtain a better optimal result and simple for use.