Though implementing feedback provided by peers has been an essential step for learning efficiency in peer feedback activities, it remains challenging for students. This study aims to explore the inner structure patterns of students' peer feedback and how they are related to feedback implementation. Sixty-nine engineering students from a Singapore university participated in the peer feedback activity. Content analysis was conducted to analyse the inner structure of feedback as well as the implementation status of each feedback. Sequential mining was applied to investigate the sequential patterns of the various feedback components. The results show a variation of inner structures in the implemented feedback and unimplemented feedback. The implemented feedback tended to be sequenced with an evaluation or a standpoint before seeking clarification or suggestions for improvement. It was also likely to contain continuous questions seeking clarifications. In comparison, the unimplemented feedback was likely to continuously indicate positive evaluations or agreements. By understanding the inner structure of peer feedback with different implementation statuses, researchers and educators can fine-tune design and instructions to support peer feedback practices.