Abstract: The performance and defect of welded joint has always been an important aspect in welding field. Previous researches mainly focus on the influence of brazing solder on welding strength. This project paid attention to the welding strength and defect of the T2 copper-45 steel dissimilar material. It was started with discussing micro-morphology of weld zone by SEM, following up with standard tensile and three-point bending experiments which were applied to obtain interface strength. In accordance with fracture toughness, a defection assessment was performed to provide the basis for enhancing welding joint strength. The results show that macro-segregation exists in the weld zone by using electron beam welding. According to interfacial strength characteristic of T2 copper/45 steel dissimilar materials, 2A level failure assessment based on BS7910 is applied and passed.