The influence of heat-treatment schedule including sealing temperature and holding time on glass-to-metal sealing behavior in terms of average pore diameter and porosity have been examined in detail by optical microscope. With increasing sealing temperature, the average value of pore diameter firstly increased, then decreased, at last increased. However, the porosity increases at first and appears constant above 980 ℃. Moreover, as the holding time prolonged, the average pore diameter increased gradually at first, and then decreased rapidly. While the porosity increased greatly, then increased slowly and decreased rapidly with increasing holding time. Additionally, increases of both sealing temperature and holding time resulted in the increase of the thickness of bubble-free layer. A spatially varying bubble structure has been presented relating profiling to processing conditions.