Abstract: In this paper, reflecting mechanism is used to model for software system requirements engineering processes.Development activities of requirements engineering processes set as base level of reflecting system complete functional requirements of software system.Nonfunctional requirements of software system set as meta level of reflecting system adjust and control development activities of requirements engineering processes.Meanwhile, the properties of nonfunctional requirements are reflected to functional requirements.The CPN and its category are defined in this paper.Simulation, preservation and reflection mechanism of nonfunctional requirements properties of the software system are stated with CPN category.Reflecting requirements engineering processes evolution formal model is created by CPN.The model simulates iteration, increment and evolution of functional and nonfunctional requirements in the software system requirements engineering processes.It presents a new approach for software system requirements engineering processes modeling.