Abstract: In recent years, leakage accidents of oil pipeline have occurred frequently. To better dispose the environmental effects of such leakage, such as river pollution, the predication of overflow process after oil pipeline leakage is critical. Considering the environmental characteristics of river waters and the overflow in river, appropriate basic control equation and hydrodynamic mathematical model are recommended, Meanwhile, overflow diffusion, drift and weathering models conforming to the river characteristics are selected to simulate the overflow movement and homing. The Fay model is improved, Navy drift model is simplified, and a new environmental effect assessment model for oil overflow into rivers is developed. Moreover, the river pollution assessment software is developed. The model and software are applied to the river sites, successfully verifying their applicability.