“功能”是一个被广泛使用的概念，也是一个没有客观和统一定义的概念。在功能模拟和智能CAD等技术的应用和发展中，急需通用和统一的功能定义及其表达体系。本文研究了一种基于特征的功能定义和符合一阶谓词逻辑的功能表达体系。 “Function” is a widely used concept, but also a concept that is not objectively and uniformly defined. In the application and development of functional simulation and intelligent CAD technology, there is an urgent need for a common and unified definition of function and its expression system. This paper studies a feature-based functional definition and a functional expression system that conforms to first-order predicate logic.