During the operation of dry gas seal, some heat（frictional heat）will be generated by viscous shear in the end face gas film, and the gas will absorb some heat(expansion heat) due to expansion when the gas flows from the inlet into the outlet.It is very importance for the design and operation of the dry gas seal to calculation the frictional heat and expansion heat quantitatively and research the heat equilibriumFor the air lubricated spiral groove dry gas seal, the calculation formula of the frictional heat was obtained by substituting equivalent clearance for the clearances of groove and land based on the concept of equal volume of the clearance, and the calculation formula of the expansion heat was obtained by solving the governing equations of film pressure modified by adiabatic exponent.The expressions of frictional heat and expansion heat varying with the film thickness were obtained by using least square fitting method, respectively.The film thickness of heat equilibrium was got by solving the heat equilibrium equationsThe variation of the film thickness of heat equilibrium along with rotating speed, groove depth, the width ratio of groove and dam and heat transfer coefficient was investigatedThe results show that the film thickness of heat equilibrium is increased gradually with the increasing of rotating speed and heat transfer coefficient, and decreased gradually with the increasing of groove depth and the width ratio of groove and dam.