In order to verify the effect of vacuum environment on the formation of pores in glass laser welding, the comparative test of glass laser welding under atmospheric and vacuum conditions was adopted.Theoretically analyze and experimentally verify of the change of porosity with laser power and the extent of expansion of glass frit to both ends under the two conditions was then carried out. The results show that, the cause of the porosity is not only the residual gas in the glass frit, but also the sublimation and decomposition of unstable components to produce more gas after the power is increased to 45W, which further improves the pores. It is found that the vacuum condition has little effect on the bonding expansion, and there is no obvious difference. The porosity under vacuum condition is significantly greater than that under atmospheric condition. The porosity is larger under vacuum condition, but the enlargement of porosity can’t enlarge the expansion width of glass frit. The results further reveal the formation mechanism of pores under laser-assisted glass frit bonding.