Oil-water relative permeability is an important parameter for studying the characteristics of water flooding development in low permeability reservoirs. It is of great practical significance to understand the percolation law in the low permeability reservoir by determining the influencing factors of oil-water relative permeability. Based on the fractal theory of porous media，a mathematical model of oil-water relative permeability in the low permeability reservoirs and a normalized oil-water relative permeability model are established respectively. The established oil-water relative permeability model is a function of water saturation，displacement pressure，and capillary pressure，which can comprehensively reflect the influence of reservoir pore structure，nonlinear percolation and percolation interference on oil-water relative permeability. The theoretical analysis result shows that the more complex core pore structure is，the lower oil-water relative permeability is；the displacement pressure influences relative permeability of oil phase，which shows that there is a dynamic change of relative permeability in the process of water flooding. Nonlinear percolation has a great influence on the relative permeability of oil phase，but the influence on the relative permeability of water phase may be ignored. The relative permeability of oil phase decreases with the increase of the nonlinear coefficient of oil phase. The percolation interference influences the relative permeability of the oil and water phase which decreases with the increase of the interference coefficient. To verify the reliability of the model，the oil-water relative permeability predicted by the model is compared with the experimental results. The predicted oil-water relative permeability of the model is highly consistent with the experimental results. In addition，the comparison with the prediction results of the classical relative permeability theoretical model shows that the prediction results of the new model for the relative permeability of water phase are better than those of the classical theoretical models.