Abstract: The wave pattern and size at ASTM S41500 Q345C interface and the welding parameters for wave appearance and disappearance at semi cylinder interface were observed and measured in explosive welding experiment with flat plate and semi cylinder as two types of base body. The results manifest that the transition velocity v_T is 1410m/s. The criterion v_T and p_C for creating wave were discussed which can be used in parameter design and weld ability window establish.