This paper examines how interpreting quality is evaluated by peer students in an English-Chinese simultaneous interpreting class. In the study, 18 students received training on how to evaluate interpreting based on three quality components: accuracy, presentation and target language quality. Then, they were asked to evaluate three translation samples by their peers and to provide comments based on the three components. After examining the collected peer comments, this paper found that there were quantitative and qualitative differences across the three components. Quantitatively speaking, peer students tended to give more comments on grammar in TL quality and fluency in presentation. Qualitatively speaking, peer students tended to give more in-depth evaluation to substitution in accuracy. The research suggests that while some easy-to-spot quality components like TL grammar may receive more peer comments, other components like substitution may stimulate peer evaluators' reflective thinking and thus should be stressed in the teaching of interpreting.