Abstract: With computational fluid dynamics method, a numerical study on effect of viaduct noise barrier height on aerodynamic characteristics of a high speed train was made. High calculation precision is obtained with suitable meshing, appropriate turbulent model and boundary conditions. It shows that as moving in leeward the side force on head train or the middle train decreases gradually with increasing of noise barrier height. A rolling moment on the head is most and it fails as noise harrier height goes up. The roiling moment on middle train running in windward is greater than that in leeward as noise barrier height is increased. Under two running conditions, the train relative position in cavity flow is different and surface pressure distribution is changed. Accordingly, aerodynamic force or moment on train body is varied.