Vertical welding is a significant welding technique in large-scale components manufacturing. With the enlargement of equipment and the increase of its reliability requirement,the development of high-efficiency and high-quality vertical welding technology is an inevitable trend. In this paper,the vertical welding is affected by gravity,which leads to poor weld formation and poor weld performance. A self-developed test platform for oscillating arc triaxial vertical welding robot system is developed. The thermal model of vertical welding process is simulated according to the pool modeling;through the comparison of welding current waveforms of the cross-section of the vertical plate under specific conditions,the effect of the molten pool on the vertical welding state in the forming process and the correction filtering method are analyzed,eliminating the influence of molten pool forming on welding wave-form and verify its feasibility,which provides a theoretical basis for studying the method of tracking welds in vertical welding.