Abstract: By taking 5 mm thick 5A06 aluminum-magnesium alloy as the main researching object,the front and back weld width as the formation parameter,the significance of torch angle to weld formation was studied by the orthogonal experiment, the effect of change of torch angle on weld formation was studied from the point of energy transfer. The result shows that the influence of the torch angle on welding formation is between current and plasma gas flow rate. There is largest front weld width when the torch is perpendicular to the test plate. The back weld width will be larger with the torch angle increasing. It indicates the energy density on the front surface,the relative position of the highest temperature section and the widest molten section will be changed by torch angle change. The effect on the back weld width may be caused by the interaction of sectional heat source deviation of different thickness direction and the delay of heat transfer.