Abstract: Grass carp Ctenopharyngodon idellus often faces the stress of overwintering in natural environment. It has been reported that fish can induce excessive production of reactive oxygen species (ROS) and cause oxidative stress during overwintering. Excessive ROS may destroy the balance and stability of antioxidant system, resulting in cell damage, nuclear apoptosis and fatty acid peroxidation. Especially during the period of overwintering, the fatty acids as the main energy supply material, have been greatly threatened and challenged because of the fatty acids maybe influenced by ROS. The most direct effect is to reduce the level of energy supply, the antioxidant capacity and immunity of the body, and increase the mortality rate, and to explore the relationship between oxidative stress and the change of fatty acid composition in tissues, In order to explore the metabolic adaptation mechanism of energy utilization of grass carp during overwintering, the initial body weight of (1053.33±16.11) g was investigated, 45 fish were randomly divided into three repetitions. When the water temperature (15℃) naturally decreased to the point that the grass carp ceased ingestion, the experiment began. When the water temperature (15℃) naturally rose to the point that the grass carp refeeding commenced, the overwintering period and our experiments were concluded. Samples were collected after 0, 1, 2, 4, 8, 12 and 16 weeks of natural overwintering. Biological indexes, antioxidant capacity of hepatopancreas, muscle, foregut, adipose tissue and serum and the fatty acid composition of hepatopancreas, muscle and adipose tissue were measured. The relationship between antioxidant capacity index and fatty acid composition was also studied association analysis. The results showed that the BW, CF, HSI, VSI, IFI and LW decreased significantly (P<0.05), while KI and SI increased significantly (P<0.05). Adipose tissue, hepatopancreas and muscle are the three tissues with the largest oxidative stress. During the overwintering period, the proportion of PUFA in hepatopancreas had a major effect on the total fatty acid composition (principal component load characteristic value >0.5), the proportion of C18﹕2n-6 and C16﹕0 in muscle had a major impact on the total fatty acid composition, and the proportion of PUFA, n-6 PUFA, SFA and MUFA in adipose tissue had a major impact on the total fatty acid composition. At the same time, association analysis showed that SFA in adipose tissue of grass carp was mainly positively correlated with oxidative stress and the fish body damage during the period of overwintering. PUFA and MUFA in muscle were positively correlated with oxidative stress and the fish body damage, while MUFA in hepatopancreas was mainly positively correlated with oxidative stress and the fish body damage. This study showed that the grass carp was subjected to strong oxidative stress during the period of overwintering, especially in adipose tissue; the fatty acid ratio of hepatopancreas, muscle and adipose tissue changed significantly, the correlation analysis with antioxidant index showed that SFA in adipose tissue, MUFA in hepatopancreas, PUFA and MUFA in muscle were related to oxidative stress have a more direct relationship between stimulation and injury. The baseline information provided in this study can be used to formulate effective feeding strategies before overwintering, and to make appropriate management and feeding decisions during the period of overwintering, and the recovery stage after overwintering and improving the survival rate and production efficiency of grass carp after overwintering.