The thermal performances of walls have great influences on the energy consumption and the thermal comfort of the room. Because the heat flux through the wall is the direct reason to cause the variations of the indoor air temperature, it directly affects the cooling/heating load and the thermal comfort of the room, the effect of the wall on the wall heat flux should be researched. In this paper, two parameters, which are the heat flux time lag and the heat flux decrement factor, are proposed to evaluate the thermal performance of the wall. Based on the one-dimensional numerical model built in the paper, the effects of the thermal properties of the wall and the thickness of the wall on the heat flux time lag and heat flux decrement factor are investigated. In addition, the heat flux time lag and heat flux decrement factor for several building materials are obtained. This research is useful for knowing the thermal performances of the wall better. (C) 2011 Elsevier B.V. All rights reserved.