In the investigation,the unsteady flow fields around the train at different model scales and different flow velocities are solved by means of the delayed detached eddy simulation ( DDES) method of the realizable κ-ε turbulence model.Then,the Reynolds number effect and scale effect of the unsteady aerodynamic characteristics of the train are discussed by changing the model scale and the flow velocity.The results show that ( 1) with the increase of the Reynolds number,the RMS ( Root Mean Square) of the aerodynamic drag coefficient of the train decreases but fluctuates obviously; ( 2) as the Reynolds number increases,the SD ( Standard Deviation) of the aerodynamic drag coefficient and lift coefficient of the train first decrease and then increase,and also fluctuate obviously; ( 3) the PSD ( Power Spectrum Density) of aerodynamic coefficients decreases with the increase of the Reynolds number; ( 4) the Reynolds number can affect the basic frequency of aerodynamic coefficients,but without obvious rules; ( 5) the aerodynamic force of trains brings about a significant scale effect; ( 6) with the increase of the Reynolds number,the scale effect of the aerodynamic force decreases,and the scale effect of the lift force becomes relatively significant; ( 7) the vibration scale effect of the unsteady drag and lift decreases with the increase of the Reynolds number,and the vibration scale effect of the unsteady lift force is more obvious than that of the unsteady drag; and ( 8) the scale effect has no effect on the vibration characteristics based on low frequencies and the PSD distribution of the aerodynamic force,but greatly affects the vibration frequency of the aerodynamic force and its PSD.