Nowadays, foreign language teaching is putting more and more attention on learners’ communicative competence. In today’s teaching process, communicative competence is often related to output practice, such as imitation, dril s, etc. This paper discusses the effects of Krashen’s Input Hypothesis on learners’ communicative competence through analyzing grammatical competence, sociolinguistic competence and strategic competence, and thus gives a further verification on effective input in foreign language teaching. Through the discussion, the study gives an implication not only for improving foreign language learners’ communicative competence, but also for the curriculum-construction and foreign language teaching and learning.