Buildings account for the largest proportion of fire sites in Taiwan. At the fire site, doors and windows are often broken for escape and fire fighting, which causes the ar-ea of dense smoke to flow inside the building to expand and cause greater disasters. Therefore, the purpose of this work is to study the size of the openings around the square structure. The influence of quantity and quantity on the combustion status of flames and smoke. This research explores this topic from three perspectives of ther-modynamics, fluid mechanics, and structure. Based on the theoretical basis of the chimney effect and the countercurrent effect of the smoke layer, acrylic is used to build a square box to simulate Buildings and experiment with the size and number of openings on the four sides of the acrylic. Two media are used for the experiment, smoke, and flame. For smoke, the MQ-2 smoke gas sensor is used to measure the concentration inside the building, and for the flame. Experiment with height and tem-perature. At the same time, CFS-MODEL’s FDS is used to simulate the interior of the building. The comprehensive physical experiment and the results show that, unlike general imagination, it is not possible to extinguish the fire by opening the doors and windows, or even because of influx Excessive oxygen will cause the fire to become more serious, the relationship between the opening area and the flame intensity is a quadratic function curve. This study can be used as a reference for fire prevention and disaster prevention during building construction, and there is the possibility of ad-vanced research.