Abstract: To obtain the optimal design satisfying strength constraints of combined structures which is composed of truss, beam, shell and membrane elements, according to fully stressed criterion and using dimensionless design variables, the approximate explicit optimization model of compined structure is founded which is subjected to strength constraints and size constraints. Taking MSC/Patran software as developing platform and MSC/Nastran software as finite elements analysis tool, the sectional area optimization program is coded by PCL(Patran Command Language). Numerical examples show rationality of the model and efficiency of the program.