The air speed distribution of grain ventilation in horizontal warehouse which is usually concerned is investigated by using CFD numerical simulation.Carefully considered air pressure distribution in the barn.Established independent numerical model for the ventilation cage of the cage ventilation method，obtained its pressure drop versus velocity data，and applied it to the full numerical model of the barn，improved the reality of the simulation.And simulated ventilation tubes in grain heaps based on the tube insertion technology from some barns.It is observed from the test result that air speed in the grain is effectively improved by reasonable arrangement of the ventilation tubes.Proposed the theory of the improvement of the ventilation effect by tube insertion and the direction of optimal designing of the ventilation tube through the observation of the flow field and pressure field nearby ventilation tubes.