Abstract: In order to make the best of the limited space in the rack to improve the heat dissipation environments of the apparatus,an analytical model of the spacelab rack was established.And by using numerical methods,the flow fields and the temperature fields inside the rack under diverse spacing of the apparatus were received.The average flow velocity and average convective heat exchange coefficient were also studied.The heat dissipation characteristics can be improved effectively by designing the spacing of the apparatus in suitable range, and this can provide the references to thermal design of racks mounted in spacelab