Abstract: The Invar alloy was brazed to SiO_2f/SiO₂ com-posite using Cu-25Sn-10Ti filler alloy. The interfacial microstructure of joint was analyzed and its formation mechanism was discussed,and also the impact of interfacial microstructure on shear strength of joints at different holding time was studied. Results show that continuous interfacial reaction layer has been formed at both sides of the base materials at brazing temperature 880℃ and holding time for 15 min,while the typical interfacial microstructure was Invar alloy/Fe₂Ti+Cu (s,s)+(Ni,Fe,Cu)₂TiSn/Cu(s,s)+Cu₄₁Sn₁₁+CuTi/TiSi+Ti₂O₃/SiO_2f/SiO₂ composite. Holding time increasing would enlarge the thickness of TiSi Ti₂O₃ layer near SiO_2f/SiO₂ composite,and Fe₂Ti particles would turn into blocks. The shear strength of joint would also change with increasing of holding time. The shear strength of the joints reaches a maximum of 11.86 MPa when the temperature is 880℃ and the holding time is 15 min.