The quality of fresh-cut Chinese water chestnuts (CWCs) rapidly deteriorates with prolonged storage time, thus affecting its commercial value. This study aimed to investigate the effect of cinnamaldehyde (CA) treatment on the quality of fresh-cut CWCs and its mechanism of action. CA treatment maintained good appearance and higher total soluble solids content (TSS) of fresh-cut CWCs and also significantly inhibited microbial proliferation, respiration, phenylalanine ammonia-lyase activity (PAL) and enzymatic browning substance content. Moreover, CA treatment increased the antioxidant capacity and defense function-related enzyme activities (PPO and POD) of fresh-cut CWCs, and suppressed ·OH production rate and MDA content. Meanwhile, CA treatment significantly increased the content of antioxidant compounds and enzyme activities of the AsA-GSH cycle system. In conclusion, CA can inhibit surface discoloration of fresh-cut CWCs and extend their shelf life, thus increasing their commercial value.