Abstract: The effects of LiF and CaF₂ in the vitreous bond have been studied by the measurement of bonding strength. The results show that, the trend of CaF₂ crystallization from Al-Si-O system vitreous bond is more obvious than that of LiF. The melting-point of the bonds is lower and the bonding force is stronger when using LiF than CaF₂ as flux. The mole ratio (Al₂O₃+B₂O₃)/(R₂O+RO+0.5LiF) can be used as a criterion to confirm the self-strength of the vitreous bonds.