So far the research of product intelligent design model focused on product function. Referring to the three principles, generality, practicability and reusability we stress that modeling for behavior meets more requirement of intelligent design model. Corresponding to product behavior we suggest the concept of behavior flow. Based on the concept we suggest the framework of product intelligent design model and adopt hybrid Petri net to describe and formulize the model of behavior flow. At last according to such theory we build a model for engine behavior to demonstrate the suggestions and methods.