In the paper

the mathematical model of multi-opening room in fire is presented. The neutral surface relation of multi-opening （with door and window both opened） room is derived by using Equality Window Dimension method. Finally

the neutral surface position of both single opening room and multi-opening room are computed and analysed when fire takes place with both door and window open.The mass flow of smoke and air under different room temperature is calcuted; and the variation of the neutral surface height is studied along with the rising of room temperature. The method for computing neutral surface position of room with multi-opening & different opening height is obtained along with the relationship between neutral surface

mass flow of smoke & air and room temperatures .The affection of air ameliorating factor on mass flow of smoke & air and neutral surface height is discussed.