Imbibition function of fluid in the fracture and matrix is a very important mechanism in low permeability reser? voir during water flooding. The oil displacement process of different low permeability cores was studied by imbibition experiment. The result shows that the imbibition process in this type of oil reservoir is an inverse imbibition controlled by higher capillary force in the system，and the capillary force is helpful to the displacement process in imbibition. The imbibition production mainly occurs in the early imbibition process，and becomes fewer and fewer after 50 h in the later period，and there is almost no production in the final period. Mostly，the imbibition oil recovery of the fractured low permeability reservoir is 12% in average and increases with the permeability. But when the permeability is more than 2×10-3 μm2，the imbibition oil recovery has few increases. Better pore structure is favorable to spontaneous imbibition. Calculated by isometric method，the experimental result may be applied to forecasting the actual oilfield development for various cores and reservoirs.