The joining of Cf/C composite to Mo30Cu alloy plays an important practical role in a bias filter for thermonuclear fusion. In this study, the Cf/C composite is joined to Mo30Cu alloy at 860 °C/10 min using AgCu4.5Ti braze after fabricating the three dimensional (3D) heat transfer interface along the Cf/C interface. The effect of interface grooving on the thermal conductivity of the joint is investigated and compared with the original brazed joint. The results demonstrate that the room temperature thermal conductivity of the joint reached a maximum of 132 W·m−1·K−1 at a grooving depth of 200 μm, which is 17.8 % higher than that of the original joint (112 W·m−1·K−1). The thermal conductivity of the joint is still as high as 100 W·m−1·K−1 at a temperature of 500 ℃. The excellent high-temperature thermal conductivity significantly reduces the Cf/C damage and extends the service life of the joint. And the shear strength of the joint has also been significantly increased by 252 % from 13.1 MPa to 33.1 MPa. Grooves prepared along the Cf/C interface provide channels for braze penetration, increasing the contact area between the brazing seam and the Cf/C matrix. Ultimately, the thermal evacuation performance of the joint is improved by increasing the heat exchange area across the joint. Also, grooves along the Cf/C interface enable mechanical interlocking with the brazing seam, achieving an enhanced joint strength. The heat transfer process of the brazed joint is simulated and analyzed by the finite element method. The analysis indicated that the thermal evacuation across the joint can be enhanced by pre-fabricating a 3D heat transfer interface in the joint. This research can provide a reference for solving the problem of heat accumulation in the first wall materials inside thermonuclear reactors.