Abstract: After long-term service, the guide vanes of K417G alloy would suffer from damages such as ablation and cracking, which can be repaired by brazing method. In the present work, the wide-gap brazing process of K417G alloy was studied by using the independently developed cobalt-based brazing filler metal, CoCrNi(W,Al,Ti,Mo,Ta)-B alloy. At the brazing temperature of 1200 ℃, the effect of brazing holding time on joint microstructure and properties was investigated. The results show that during the brazing process, mutual diffusion occurred between the filler alloy and the K417G base material, forming wide-gap brazed joints with good metallurgical quality. The microstructure of the brazed joints is composed of superalloy skeleton powder particles and the brazing filler alloy connection zones between the particles. The filler alloy connection zones contain a gray matrix and a white precipitated phase. The gray matrix zone presents a γ+γ' duplex structure, while the white phase is composed of borides. The microstructure morphology characteristics of the joints are similar under different holding times, and the endurance life shows a trend of first increasing and then decreasing with the extension of holding time.