Abstract: Targeting at the diffusion of leaked oil for rivercrossing pipeline, finite volume method and k-ε turbulent flow model are chosen to build a numerical simulation model of small hole leakage of river crossing pipelines. The diffusion process of diesel in water is simulated. The volume fraction and diffusion range of diesel under different leak hole diameter, leaking velocity and flow velocity of water are analyzed and compared. The results show that leaking velocity, diameter of leak hole and flow velocity of water can not only directly affect the diffusion trajectory and migration manner of diesel in water, but also change the volume fraction and diffusion range of diesel in water. This research can provide a theoretical reference to the construction of emergency prediction system of leakage accident of river crossing pipeline.