Abstract: For a specific duct, its hydrodynamics feature was simulated and analyzed by using Fluent software. The thrust force, thrust coefficient, lift-to-drag ratio and flow distribution of the duct design under different conditions of different contraction coefficients, expansion coefficients, parallel, length-to-diameter ratio were compared. Through the above analyses and calculation, we can get the optimal duct shape, which meets all requirements. Comparisons to the experiment results show that the numerical method is effective.