Research on peer assessment in higher education has been conducted for decades. However, ways to improve the quality of peer feedback and optimise student' benefits through peer assessment remain a puzzle. The present study aimed to examine the impacts of synchronous discussion between assessors and assessees on writing performance, qualitative feedback quality, meta-cognitive awareness and self-efficacy in web-based peer assessment. A total of 64 undergraduate students participated in the study and were randomly assigned into either the experimental or control group. Participants in the experimental group conducted synchronous discussion after the first round of peer assessment, while students in the control group did not conduct any synchronous discussion. The results revealed that synchronous discussion between the assessors and assessees significantly improved the students' writing performance, especially content writing skills, affective and meta-cognitive feedback quality, meta-cognitive awareness and self-efficacy. Practical implications, limitations and future directions are discussed based on these findings.