Disruptive innovation is an effective process of product innovation, and the analysis of disruptive technological opportunities is an entry point of developing disruptive innovative products. Based on the fact that the sub-functions of a product get different degree of attention from customers or engineers, a construct of functional role is introduced and a classification is proposed. According to the definition and characteristics of new market disruptive innovation, functional roles of functions that a product has are adjusted, and an approach to identify some disruptive technological opportunities of mechanical products was proposed. Finally, air conditioner was taken for example, and the generation of disruptive innovative opportunities verifies the feasibility of the approach.