Second language acquisition is the process involved in the interactivity between the learners and other target-language users. In this process, such factors as the language proficiency and ways of feedback will all have different influence on the output of the interactivity. This paper studies the effects of negative feedbacks (implicit feedback, error correcting and explicit feedback, error pointing out) of speakers at different proficiency levels (teachers and peers) on the output ability of language learners, and discussion on effectively using feedback ends the paper.