Transient liquid phase bonding is employed to join China low activation martensitic (CLAM) steels, with Ni-based amorphous foil as interlayer. The effects of the Ni-based amorphous foil on the microstructure and mechanical performance of the joint are investigated. During bonding, as the temperature reaches to the start temperature of austenite transformation, boron, a melting point depressant in amorphous foil, can diffuse along austenite boundaries, resulting into compounds containing boron and the fine-grain zones adjacent to the interlayer. Owing to the melting of interlayer and the dissolution of substrate material, the final width of the interlayer is increased. Moreover, at the interlayer close to the joint interface, small voids can be observed, associated with the difference between Fe and Ni in diffusion rates. It should also be noted that the bonded CLAM/CLAM steels always fracture at the interlayer.