In recent years, with the development of industrial production, the repair and bonding of wide gaps has always been a key technology. In this study, a gap (width of 20 mm) was bonded by wide gap brazing technology. The K417G superalloy was used as the base metal, and a mixture of low-melting powder (LMP) and high-melting powder (HMP) was used as the filler metal. In this research, K417G superalloy was brazed by different contents of LMP + HMP mixed powder. The microstructure evolution and mechanical properties of joint was analyzed. With increasing the ratio of HMP in the filler metal, the borides in the joint was decreased and the uniformity of composition and microstructure of joint was improved. When the ratio of HMP in the filler metal increased to 95 wt.%, B can be uniformly diffused into the HMP and brittle borides at the interface were significantly reduced. The tensile strength of the joint at room temperature and 600 °C was 971 MPa and 934 MPa, reaching the strength of base metal. In addition, the fine particles of M23(C, B)6 carbon-boride are coherently precipitated in-situ in the joint and uniformly dispersed, facilitating excellent repair.