Low-permeability oil reservoirs typically require fracturing technology for production enhancement. However, the artificial fractures created by fracturing exacerbate reservoir heterogeneity, leading to issues such as injected water channeling and rapid water breakthrough in production wells. This results in inefficient oil mobilization and low recovery rates. To investigate the impact of fractures on water-flooding development in low-permeability oil reservoirs, a physical simulation experiment was conducted. The relative permeability curves of oil and water were measured using cores with different permeabilities and fracture lengths. Based on these curves, the dimensionless liquid productivity index and dimensionless oil productivity index were calculated. A chart illustrating the influence of reservoir physical properties and fracture length on liquid and oil productivity was established, and the distribution patterns of remaining oil after water flooding were revealed. The results indicate that fractures have a dual effect: enhancing permeability and causing channeling. In low-permeability reservoirs with poor physical properties, fractures significantly improve flow capacity and promote the movement of oil and water. However, they also intensify reservoir heterogeneity (as indicated by an increase in the fracture-to-matrix permeability ratio, Kf/Km), making injected water prone to channeling along the fractures. This leads to a sharp rise in the dimensionless liquid productivity index, with remaining oil primarily concentrated in the central part of the core and on both sides of the fracture. For reservoirs with the same physical properties, an increase in fracture length expands the controlled range, enhances oil displacement efficiency, and improves recovery. However, it also further intensifies reservoir heterogeneity and channeling, causing premature breakthrough of injected water. This results in a rapid increase in water cut and a swift rise in the dimensionless liquid productivity index, with remaining oil accumulating near the fracture at the production end of the core. This study provides theoretical and technical support for optimizing fracturing development and designing water-flooding strategies in low-permeability oil reservoirs.