Fire-whirl is a specific fire behavior, and has been taken as one important research area of fire safety. The earlier relative studies are mainly focused on the experimental reproduction of swirled flame and numerical simulation for the flame itself. However the behavior of fire-whirl is much different from the pure swirled flame. It is constructive to conduct performance-based fire protection analysis and design to understand these behaviors scientifically. In this paper, the behavior of building fire-whirl is studied, and an analytical method to describe and express the center shift phenomena of the building fire-whirl is presented. Combined with such method, the large eddy simulation (LES) technology is employed for numerical simulation of the center shift of fire whirl, and the important parameters such as average angular velocity, peak of temperature, location of the high-temperature center are obtained.