Abstract: Kovar alloy and DM308 glass were bonded with YLS-6000 fiber laser. The effect of interlayer on the strength, interface structure and interface bonding mechanism was investigated. The diffusion behavior of interface elements is analyzed. The results showed that the Mo-Mn-Ni interlayer can reduce the cracks at the edge of the joint,and Ni₂O₃-MnO₂-B₂O₃ interlayer can reduce the number of micro cracks and the number of bubbles on the glass side. The weakest part of the 4J29 / DM308 laser welding joint is near the glass side, which breaks through the bubble. The biggest shear strength of Mo-Mn-Ni interlayer joints is 10.96 MPa. The biggest shear strength of Ni₂O₃-MnO₂-B₂O₃interlayer joints is 13.46 MPa. The thickness of Ni₂O₃-MnO₂-B₂O₃ interlayer transition layer is about 30-40 μm. There is obvious dendrite growth in the transition layer. The results of joint interface XRD phase analysis show that the interface transition layer is FeSiO₃ and Fe₇SiO₁₀. It is belong to Fe and Si cubic complex oxides. The results of EDS analysis showed that Fe, Co, Ni, Al, Na and Si elements had diffused in the whole interface region. The interfacial bonding mainly depends on chemical reaction and element diffusion.