Abstract: Reduced activation ferritic/martensitic (RAFM) steels and vanadium alloys are considered as candidate structural materials for the first wall of fusion reactors in the future, with their own advantages and disadvantages, which can meet the requirements of short-term and medium-term applications. In this study, hot isostatic pressing technology was used to connect V4Cr4Ti alloy and RAFM steel CLF-1 at the hot isostatic pressure parameters of temperature 800 ℃, isostatic pressure 150 MPa and holding time 2 h, and the interface microstructure, element diffusion characteristics and shear mechanical properties were analyzed. The results show that a decarburized layer is present in the CLF-1 steel within a distance of 120 μm from the connection interface, while a high-hard brittle carbide layer with a width of about 1.5 μm exists on the V4Cr4Ti alloy side. The V4Cr4Ti alloy/CLF-1 steel connection interface has no defects, and the room temperature shear strength of the joint is up to 238 MPa. The fracture analysis results show that the fracture occurs in the high-hard brittle carbide layer at the vanadium alloy side, and the fracture shows the characteristics of overall toughness and local brittle fracture.