Based on the characteristics of spatial structure of residential units, the law of indoor hot smoke flow was investigated by experimental research on a platform model with multiple floors and rooms in a residential building. Three factors exerting influence on hot smoke flow in residential construction were mainly analyzed, including the relationship between the height of space and the area of single room, the size of doorway opening, and the hub space. Based on basic concepts of thermodynamics and fluid mechanics, the geometric relational model of the height of space and the area of single room impacted on filling speed of hot smoke in room was presented by conservation of mass. Moreover, under the influence of hot smoke flow, the formula of doorway opening size was developed by conservation of momentum. The results show that the fire safety of residential building should take full account of the impact of spatial structural. The indoor temperature distribution and hot smoke flow path will be controlled effectively by the design of single room size and room connectivity.