Abstract: A three-dimensional physical model of an air supply device for a rail transit air conditioner was established, which was composed of a cross-flow fan, a diffuser and a heat exchanger. Its grids were divided in the finite element preprocessing software Hyper Mesh. Fluent fluid calculation software was used to perform CFD simulation calculation for the system of the device. The flow velocity in the fan and the surface velocity distribution of the outlet heat exchanger were analyzed, which provides theoretical basis for improving air supply system and air conditioning comfort.