The present invention relates to the field of reliability-based structural design optimization, and provides an integration method for accurate modeling and analysis and reliability-based design optimization of variable stiffness composite plate and shell structures. In this method, the first-order reliability method, two-point adaptive nonlinear approximation and second-order reliability method are applied into the efficient reliability-based design optimization of variable stiffness composite plate and shell structures. The fiber placement path of variable stiffness composite plate and shell structures is accurately modeled by non-uniform rational B-spline function. Isogeometric analysis is utilized for the variable stiffness composite plate and shell structures, including conducting linear buckling analysis on the variable stiffness composite plate and shell structures based on the isogeometric analysis method and deriving analytical sensitivity of design and random variables on the structural response. This invention not only provides seamless integration of accurate modeling, analysis and reliability-based design optimization of variable stiffness composite plate and shell structures, but also significantly improves efficiency and accuracy of reliability-based design optimization and greatly shortens the development cycle.