充要条件是重要的数学概念 ,它揭示了命题的条件与结论之间的逻辑关系 .充分条件与必要条件的判定一直是教学的难点 ,对于初学者来说 ,主要原因一是对概念的理解不够深刻 ,二是解决问题的方法不够恰当 .下面结合个人多年的教学实践 ,从不同角度给出充要条件概念的两种理解方法 The necessary and sufficient condition is an important mathematical concept. It reveals the logical relationship between the conditions of the proposition and the conclusion. The judgment of sufficient conditions and necessary conditions has always been a difficult teaching point. For beginners, the primary reason is the understanding of the concept. Not profound enough, and secondly, the method of solving the problem is not appropriate. Following the teaching practice of individuals for many years, two understanding methods of the concept of necessary and sufficient conditions are given from different perspectives.