RANS approach is adopted to perform an investigation on aerodynamic characteristics of high speed trains in crosswind conditions. Both the flow structures and aerodynamic loads are analyzed in detail. Results reveal that abundant flow phenomena could be observed on the streamlined head and affected by the yaw angles of the incoming flow. Detached vortices can be found on the leeward side of train, which origin from the bottom of the streamlined head and develop along the train body and gets far away from the train body. The first car of the whole train owns the worst aerodynamic circumstance. As the yaw angle grows, the side force and the overturning moment of the first car gradually grow bigger, and the running circumstance of the train becomes worse.