Abstract: A novel welding process with molten metal filler is invented to solve the problem of controlling the welding heat input and to suit the require of high-efficient manufacture. The design and principle of welding system and its elements are mainly introduced. Meanwhile, testing the system by overlaying weld using tin-lead alloy. The results show that the system accurately control welding heat input by output steady flow with required temperature and diameter, welding speed and air pressure. Therefore, the system could meet the requirement of welding process with molten metal filler, and the depth-to-width ratio of bead can reach 6 by using it.