In order to interpret the characteristics of the thermal flow field and swirling flames in an enclosure, an experiment in a quadrate shaft having size of 2.0m×2.0m×15.0m with a single corner gap was conducted, and the temperature along the central axis of the shaft was measured. Besides, in order to verify whether or not the numerical method with Large Eddy Simulation (LES) is able to predict the thermal flow field, the predicted temperature was compared with the experimental data. Furthermore, the distributions of average pressure, temperature, and density along the lines of height and radius are obtained, when the fire swirl is steady. And the barocliny of the swirling flames due to buoyancy is analyzed. The stratification of the temperature and pressure with height are concluded. These results provide a reference for the research on the swirling flames driven by buoyancy in an enclosure.