The aim of this study was to investigate the protective effect and its mechanism in the context of antioxidant of flavonoids from Zostera marina (ZF) on chronic alcohol hepatic injury in mice. This study would provide scientific basis for the prevention of chronic alcohol hepatic injury. ZF were extracted by the combination of cellulose and ultrasonic wave assisted and purified by polyamide resin column chromatography. The scavenging DPPH and hydroxyl free radicals abilities of ZF were studied. To establish chronic alcohol hepatic injury model, 60 ICR mice were randomly divided into 6 groups (10 mice per group): normal group (C), model group (M), positive group (P), FL group treated with ZF at dose of 40 mg/kg?d, FM group treated with ZF at dose of 80 mg/kg?d and FH group treated with ZF at dose of 160 mg/kg?d. Mice in normal group were treated with distilled water by gavage, and mice in other groups were treated with 50% alcohol by gavage. 60 min later, mice in normal group and model group were given distilled water, positive group mice were given bifendate and other group mice were given ZF of different doses. After 6 weeks of treatment, all mice were killed and blood samples were taken to measure the activities of ALT, AST, γ-GT and the contents of TC and TG. And liver was taken to detect the activities of GSH-Px, SOD, ADH, ALDH and the content of MDA. The ZF flavonoids content reached 80% after purification. The antioxidant activity of ZF was evaluated by in vitro experiments. In vivo experiments, the liver index of model group was significantly increased, while the liver index of ZF treated groups was significantly lower than that of model group. These results suggest that ZF have some protective effect against alcohol hepatic injury. The activities of ALT, AST, γ-GT and lipid levels in serum and the MDA content of liver in model group significantly increased; the activities of GSH-Px, SOD and ethanol metabolic enzymes of liver in model group evidently decreased, indicating that chronic consumption of alcohol resulted in a serious hepatic injury in mice, and the model of chronic alcohol hepatic injury of mice succeeded. Compared with model group, ZF groups significantly reduced the activities of ALT, AST, γ-GT and lipid levels in serum, the content of MDA in liver increased the activities of GSH-Px, SOD and ethanol metabolic enzymes. The results show that ZF protected mice against chronic alcohol hepatic injury by increasing antioxidant capacity, regulating lipid metabolism and alcohol metabolism. Long-term excessive drinking can lead to hepatic injury; ZF have protective effects against chronic alcohol hepatic injury, and the mechanism is related to antioxidant capacity, lipid metabolism and alcohol metabolism.