Abstract: The overall wettability of tight oil reservoir rock and the wettability of its different sizes of pores were studied based on the mineral distribution around pores and the fluid distribution characteristics in different sizes of pores. Firstly, the mineral distribution characteristics around different sizes of pore throats in tight oil reservoirs were researched on the basis of scanning electron microscope (SEM) experiment. Then, the distribution states of fluid after flowing into the pores of tight oil reservoirs were investigated by means of spontaneous imbibition and nuclear magnetic resonance (NMR) experiment. Finally, based on the mineral distribution characteristics around pores, overall rock wettability and pore throat wettability were analyzed by using the imbibition curve and NMR T₂ spectrum distribution after the imbibition of the rock in water phase and oil phase respectively. It is indicated that around the large pores in the target core are mainly carbonate minerals and around the small pores are mainly clay minerals and silicate minerals. What’s more, spontaneous imbibition and NMR experiment verify each other, indicating that the rock is overall prone to water wettability, specifically water wettability prone in large pores and water wettability prone in small pores. This research provides a new idea for evaluating the overall wettability of tight oil reservoir rocks and the wettability of their different sizes of pores.