In order to obtain digital design of complex mechanical product as optimal as possible in an efficient way, multidiscipline integrated design method is proposed, which integrates multidisciplinary design optimization (MDO) into digital design process to design virtual prototype (VP) efficiently. Through combining MDO and multi-body system dynamics, MDO integration platform, which takes VP as the core, is constructed. Then automated MDO design of VP is realized and changes of mechanical design project can be expressed intuitively during MDO design process. The proposed approach is also demonstrated by using integrated analyzing flow of vehicle engineering design. The result shows that the method not only can feasibly realize the MDO of VP, but also can solve the optimization problem of vehicle multi-body system dynamic performance. It can be adopted to the digital design of other complex system.