Abstract: Three on ground test methods for simulating the gas convection,heat and mass transfer in the cabin of spacecrafts,have been analysed theoretically and discussed in the present paper,including thermal reducing scale modelling,reducing pressure modelling and mass convection comparison modelling.The laws or criteria of similitude and their application constraints in accordance with different simulating test methods are given.Their advantages and disadvantages were compared in principle.It is indicated that:(1)thermal Reducing scale modelling can obviously reduce the influence of natural convection if reynolds number is constant,but this test method can not be used for an engineering model;(2)reducing pressure modelling can be used for an engineering model,however,it can not be used for liquid flows:(3)mass convection comparison modelling can completely eliminate the natural convection,but it is very complicated and difficult in engineering applications.