In order to support a question-answer driven simulation process, a design process model is introduced to describe problem statements, model specifications, simulation models and problem answers as separate objects. This method can effectively solve the engineering problems related to product design and technical performance, reduce modeling complexity and realize trace-ability on an object-to-object level of information. Then it conducts an applied study on performance matching of the hydraulic system in a large excavator. By the question-driven modular modeling, the working performance under lifting, digging and horizontal pushing operating condition, the power consumption of the hydraulic system and the influence of the performance matching parameters are simulated and analyzed. The results demonstrated that it was a practical valid method for process modeling of complex product, and it can accurately assess the excavating performance, provide the decision basis for the further design.