Abstract: To solve the problems of excessive brittle compounds at the interface and high residual stress which easily leads to cracking in the active brazed joint between SiO_2f/SiO₂ composite and sapphire, a CNT-AgCuTi composite interlayer was designed and prepared for auxiliary brazing. The results show that the in-situ reaction between CNT and Ti element during brazing effectively inhibits the formation of agglomerated TiCu brittle phase, and a large area of Ag(s, s) + TiC structure, as well as a small amount of TiCu₄ phase is formed in the brazing seam. Continuous and dense reaction layers are formed at the interfaces between the SiO_2f/SiO₂ composite and sapphire, and an Ag-Cu eutectic structure with excellent plasticity and toughness is formed near the interfaces of the two base materials, which is conducive to relieving the residual stress of the brazed joint. Under the brazing parameters of 880 ℃/10 min, by using the CNT-AgCuTi composite interlayer with a mass ratio of 10∶4 for auxiliary brazing of SiO_2f/SiO₂ composite and sapphire, the shear strength of the brazed joint is increased from 3 MPa to 26 MPa. This method can provide experimental and theoretical bases for regulating the interfacial microstructure and improving the joint performance in other active brazing systems.