Abstract: The synchronous linkage welding of steel-aluminum hybrid radiator with multi-vertical-tube and intersecting line weld was conducted with double welding torches. The mathematical models of the intersecting line weld seam for T-type cylinder tube and the posture of double welding torches were established in the independent development process of four-axis complex linkage automatic welding machine with double welding torches for avoiding obstacles. By applying VC++,the corresponding relationship between the rotating angle and time was derived in interpolation period. Based on the trajectory characteristics which were achieved by the terminal executor of the synchronous linkage welding system with double welding torches,the trajectory planning was executed and three-dimensional model was established in Pro/E environment to simulate the movement to check whether the welding torches and radiator aluminum wing interfered with each other. The welding experiments show that the mathematical model of the intersecting line weld seam and the welding torch posture could be applied to accurately weld the intersecting line and enhance the production efficiency and welding quality.