The main goal of this project is to study and develop theories and methods for design optimization of ultralight materials and structures. The main contents of the researches include: 1) Study the formulation and solving methods for topology optimization of engineering structures under the coupled action of multi-physical fields, considering the nonlinear properties, and with multi-functional requirements (constraints); 2) Based on the bionic analysis ideas, through observing and analyzing the characteristics of the natural bionic materials and structures, to establish the bionic analysis and design optimization models of the mechanical and heat transfer properties of structures; 3) Combine bionic analysis with topology optimization of structures, investigate the formulation of the design optimization problem of which the design variables includes microscale (microstructure representative parameters) and macroscale (structural geometric parameters) parameters, and propose an integrated design optimization method of material design and structural design; 4) Study and develop theoretical methods for predicting the effective properties of composite materials considering the influences of the micro-buckling, micro-flow and heat transfer in microstructures; 5) Investigate and establish the design theories and methods of ultralight materials with specific properties, and obtain some kinds of typical microstructures of ultralight materials with typical properties (such as, materials with specific elasto-plasticity, damping properties, heat transfer performances, etc.); 6) Find and investigate the difficulties in sensitivity analysis and optimization caused by different scale levels of the design variables, develop the methods for sensitivity analysis and optimization; 7) Considering the uncertainty and discreteness of the representative parameters of microstructure of material and macroscale geometry of the structures, study and determine the stochastic characters of the effective properties and the relationship of the macro properties with the microstructure of materials.