This study experimentally investigates oil-water relative permeability curves in low-permeability reservoirs, with particular emphasis on the influence of capillary pressure. Using three core samples with varying permeability levels from a specific block of the Changqing Oilfield, displacement experiments were conducted under reservoir conditions (65 ℃, 20 MPa) via the unsteady-state method. A modified JBN method incorporating a capillary pressure gradient term was proposed to improve the accuracy of relative permeability calculations. The results indicate that core permeability is negatively correlated with both irreducible water saturation (Swc) and residual oil saturation (Sor). As permeability decreases, capillary forces become more significant, restricting oil phase flow and leading to higher relative water permeability at residual oil conditions. The modified JBN method significantly enhances the accuracy of oil relative permeability estimation, especially at low water saturations. This study provides both experimental and theoretical support for understanding oil-water flow behavior in low-permeability reservoirs.