Abstract: In selecting rational types of underground structures resisting explosion,in order to improve stress states of the structural section and make full use of material strength of each part of the section,the research method of composite structures is presented. Adopting the analysis method of micro-section free body,equilibrium equations,constraint equations and deformation coordination equations are given. Making use of the concept of generalized work and directly introducing Lagrange multiplier specific in physical meaning,the validity of the constructed generalized functional is proved by using variation method. The rational rigidity matching relationship of composite structure section is presented through example calculations.