The technology of sealing glass ampoule by preheating, melting and sealing by CO2 laser was presented in this paper. The ANSYS software was used to simulate the temperature and thermal stress distributions considering the influences of surface convection and the variation of the physical properties of the glass with temperatures. The relationships between temperature and the thickness and rotating velocity of the ampoule were obtained. The results show that the surface temperature decreases with the increase of thickness; the temperature of the outer surface will reach almost the same value at different rotating velocities, if the laser interaction time is the same. The main cause of the ampoule broken is the tensile stress during the cooling.