A large amount of water-based fracturing fluid containing dissolved oxygen needs to be pumped into the formation for hydraulic fracturing in shale gas reservoirs，but the flowback rate of fracturing fluid is generally lower than 30%.The analysis on water imbibition mechanism plays an important role in interpreting the distribution behavior of fracturing fluid leak-off. The organic-rich shale deposited in the hypoxic reduction environment is prone to oxidation reaction under the oxygen-rich condition，however，the effect of oxidation dissolution on the imbibition behavior is still unclear. The shale outcrop samples from Longmaxi Formation in Sichuan Basin were selected in this study，then the experiments of spontaneous imbibition of distilled water and oxidative fluid were carried out in large-scale shale samples successively. And the spontaneous imbibition of distilled water into shale plug samples were performed，exploring the change in water imbibition behaviors in the plugs before and after the treatment of oxidative fluid. The results showed that compared with distilled water，oxidative fluid accelerates the propagation of microfractures and generation of new fractures，promoting more soluble salt to separate out along the microfractures，and showing a larger distribution range of water phase. The imbibed water masses of shale plugs with parallel and perpendicular bedding are 0.425 0 g and 0.446 1 g before oxidation，and they are increased to 0.490 0 g and 0.497 8 g respectively after oxidation. Similarly，the imbibed water masses of shale plugs with fractures are 0.991 2 g and 0.950 0 g，and they are increased to 1.088 6 g and 1.066 9 g respectively after oxidation. The oxidation increases the imbibition capacity of shale plug with matrix by 11.6%-15.3%，and the imbibition potential is increased by 2.32%-8.26%. The imbibed water masses of shale plugs with fracture are increased by 9.8%-12.3%，and the imbibition balance time is decreased by 13.68%-20.23%. The results indicated that the net material removal effect of oxidative dissolution on shale components enlarges the storage space of water phase，improves the porosity and permeability，enhances the water wettability of fracture surface，induces the generation and propagation of microfractures，and decreases the saturation of imbibition front，accelerating water diffusion and increasing the imbibition distance.