Abstract: Oil pipelines are characterized with long mileage, high risk of transportation medium and complex hydrogeological conditions. Once oil leaking occurs in environmentally sensitive areas, serious environmental pollution may be caused. Taking a high consequence area of an environment as example, a conceptual model, a water flow model and a solute transport model were established on the base of Visual-Modflow software to simulate the migration and diffusion law of petroleum hydrocarbon in groundwater under the situation of oil pipeline leakage. The state of groundwater was early warned with the improved Nemero comprehensive pollution index method, and the early-warning level of different wells was determined according to the relationship between the change rate of water quality and the early-warning level. As indicated in the results, evaluation on early warning of the pollution risk of groundwater in case that leakage occurs to an oil pipeline, could effectively pre-warn the leakage of oil and predict the diffusion trend of the leaked oil of the pipeline.