Krashen的可理解性输入理论是二语习得的重要理论之一。课堂教学是留学生可理解性语言信息输入的主要来源。本文从可理解性输入理论入手,讨论了输入与输出的关系,认为目前汉语课堂教学普遍存在输入不足的情况。在组织课堂教学时教师应有较强的输入难度调控意识,注意语言素材的组织和铺垫。文章最后提出运用可理解输入需要注意的几方面因素。 Krashen’s intelligibility input theory is one of the important theories of second language acquisition. Classroom teaching is the main source for foreign students to understand the input of language information. This article begins with the theory of intelligibility input, discusses the relationship between input and output, and concludes that there is a ubiquitous lack of input in current Chinese classroom teaching. When organizing classroom teaching, teachers should have a strong sense of control over input difficulty and pay attention to the organization and development of language materials. The article concludes with several factors that need attention to understandable inputs.