Abstract: The air flow field in a large spacecraft was analyzed by the method of numerical simulation under conditions of low velocity, room temperature and laminar flow's assumption. Effects of the condenser, air cleaner, fans and other objects in the spacecraft on the air flow field were observed, and corresponding influences of flow field to distributions of temperature, humidity and carbon dioxide concentration inside the spacecraft were presented. Accordingly, the transport of mass and energy by airflow was evaluated and a theory of whole-flow-field-design in the large spacecraft was brought forward. In this theory, a novel design to construct the whole flow field with circumfluent and the partial flow field cooperating with diffusion of mass and heat was emphasized, from the whole system point of view. That was, equipments in spacecraft must be arranged in specified place to result in circumfluence in the whole flow field, and the partial flow field was designed to cooperate with diffusion of heat, water and carbon dioxide source. Comparisons of some parameters e.g. average velocity and velocity un-uniformity coefficient of flow, were carried out between the recoverable module and the orbital module of the spacecraft, and the results well approved the novel theory above.