Planar movable tooth drives have a compact structure. However, as the size decreases, the heat dissipation capacity decreases; therefore, temperature control is required. A heat conduction model of the drive system, including the central wheel and movable tooth, is established, and the meshing point of the movable tooth and center wheel is considered the heat source. The heat flux density at the meshing point is determined, and the analytical equations describing the temperature increases of the center wheel and the movable tooth are derived. The effects of the input power and system parameters on the temperature increase of the system are analyzed. The results show that the temperature difference of the movable tooth is about 1.5 times the temperature of the center wheel, and the temperature increase near the heat source decreases by more than 15 °C as the movable tooth radius increases from 2 mm to 2.5 mm. The movable tooth radius and center distance have significant effects on the temperature increase and can be used as control parameters to prevent a temperature increase of the drive.