To study effects of heat treatment on the in vitro digestion characteristics of tuna meat and the antioxidant activity of the digests， unheated and heated tuna meat were simulated for gastrointestinal digestion， and the digestibility， molecular weight distribution， antioxidant activity and the degree of hydrolysis （DH） of the digests were analyzed. In addition， the solubility of tuna meat in different solvents before and after heat treatment and its pattern in SDS-PAGE were analyzed to clarify the mechanism of the effects of heat treatment on the digestion characteristics， antioxidant activity and structure of tuna meat at the molecular level. Results showed that after heat treatment， the digestibility of tuna meat was 21.72% lower than control group and DH were significantly lower than that of the control group （P＜0.05）. During the digestion process， the content of peptides with molecular mass less than 1 ku increased gradually with the extension of digestion time. The maximum value was obtained after 4 h， but the content of the heat-treated group was significantly lower than that of the control group （P＜0.05）. At the same time， the antioxidant activity of the digests in heat treatment group was lower than that of the control group at different time， and the scavenging ability of ABTS free radical after 4 h digestion was 931.56 μmol TE/g and 1 028.90 μmol TE/g， respectively， indicating that heat treatment is not conducive to the digestion of tuna meat and releasing small molecule antioxidant peptides. The solubility of tuna meat in different solvent was significantly lower than that of the control group（P＜0.05）， indicating that new covalent bonds were formed during the heat treatment process of tuna meat. In addition， the degradation of protein subunits was observed in SDS-PAGE electrophoresis. The results showed that heat treatment caused thermal denaturation and degradation of tuna meat protein， and new covalent bonds were formed， which changed the structure of protein and thus reduced its digestion efficiency and the release of small molecule peptides with antioxidant activities.