Abstract: As Lancang River crossing is the "throat project" of the entire China-Myanmar Crude Oil Pipeline, it is very important to guarantee its safe operation. Based on the outline of the two-dimensional river map of the downstream of the Lancang River crossing section, a two-dimensional calculation domain for the downstream river course of the oil spill accident in the crossing section was established. Using the SST k-omega turbulence model and combined with the VOF method of tracking the multiphase flow interface, simulation calculations were performed for a total of 12 leakage scenarios of different river water periods, different leakage locations, and different leakage modes. In the 12 leakage scenarios, the amount of crude oil leakage in the Lancang River was considered as the maximum, the diffusion and distribution of crude oil on the surface of the river and the diffusion distance of the crude oil in the direction of the river were analyzed, and the migration and diffusion laws of crude oil in Lancang River with the influence of various factors were summarized. The simulation results are of strong reference significance for predicting the location of crude oil diffusion and the release of oil booms on site, and could provide strong technical support for emergency treatment of oil spills and environment protection in the Lancang River crossing section.