"Monitor Model" explains the process and its situation from five different parts: the acquisition/learning,monitor, natural order, input, and affective filter. The Input Hypothesis, as one part of"Monitor Model" proposedby Stephen D. Krashen, suggests that the comprehensible input plays a key role in the language acquisition.Nowadays, the Input Hypothesis, with "i+l" as its core proposal, influences Chinese foreign language teachingfrom various aspects. But there are also many disputes. In this paper, the author intends to elaborate on its maincontents, characteristics, influences on foreign language teaching, existing defects, and so on, aiming to achieve thegoal of reviewing of this theory and its influence in China.