To study the frictional heat of the asperity on friction pair of the inner and outer rings of spherical plain bearing during relative sliding process, the model of a hemispherical asperity sliding relative to a smooth plane is established. The steady-state temperature rise of the inner and outer rings in the asperity contact zone is calculated with integrating the temperature rise caused by point heat source. The temperature rise distributions of the contact zone under elastic contact and plastic contact were calculated respectively, and then the temperature rise along the velocity direction under different angular velocities and loads was examined. The maps of the maximum flash temperature in the contact zone of two different types of spherical plain bearings are presented. The results show that the temperature rise of the asperity in contact zone is symmetrically distributed, and the maximum temperature rise is at the center point. The temperature rise at the trailing edge of the outer ring is greater than that at the leading edge, and the maximum temperature rise appears at the position of trailing edge. The higher the angular velocity or load, the higher the temperature rise. Under low-speed and heavy-load conditions, the maximum flash temperature of the asperity is low, and in case of high-speed conditions, the maximum flash temperature is high. To prevent the spherical plain bearing from being damaged due to excessive heat generation caused by asperities, the control of loads and angular velocities should be noticed.