The gas flow distribution in electrostatic precipitator(ESP) ducts of a thermal power plant was numerically simulated with CFD. On the basis of the middle experiment model, Gambit and ICEM CFD were used to create mesh. CFX and Fluent were used to conduct the numerical simulation. The simulation results are in good agreement with the experimental data in ESP ducts with or without turning vanes. The simulation results can be used to guide the models and the adjustment of the turning vanes in the thermal power plant in order to obtain uniform distribution of gas flow in ESP ducts.