Abstract: In consideration of the flow field characteristics of car aerodynamics,three-dimensional incompressible Navier-Stokes equations and RNG k-ε(renormalization group k-ε)model were used in simulation.Second-order upwind difference scheme was applied to obtain the physical quantities of control pedal,and SIMPLEC method was adapted for iteration.Different car model proportions and wind tunnel cross sections were simulated,the effects of car models proportion and wind tunnel cross section on aerodynamic characteristics of car were analyzed.The results show that: in a certain range of car models proportion,aerodynamic parameters of car changes gently;the simulation results of different car model proportions in three typical wind tunnel models vary greatly.