Based on investigations into the flow field of ducted fan aircrafts, structural parameters of duct are quantified. A three-dimensional model is established for numerical simulation, and adaptive Cartesian grid is used to mesh the model in order to improve calculation speed and solution accuracy. Three-dimensional Navier-Stokes equations are brought in to analyze different duct styles. Generalization of simulation results leads to several conclusions in duct aerodynamics to help design ducted fan aircrafts.