Aimming at the building envelopes in the radiant cooling and heating system,this paper analyzes the relationship between the thermal storage performance of radiant surface's materials and start-up or shut down time of heating and air-conditioning system.The impact of the external walls with different number and different types on indoor thermal environment is studied.It comes to the conclusion that the thermal storage coefficient of radiant surface's materials is greater,which will lead to better thermal stability,the longer lag time in temperature change.The external walls with different number will cause larger changes in indoor thermal environment.With the increase in the number of external walls,floor surface temperature should be raised in order to meet the requirements of indoor comfort.