Abstract: Medium plate with T-fillet joints and one-side V-shaped grooves has the characteristics of low cost and high production efficiency. However, the two sides of the weld are asymmetrical, especially the thickness of the root structure is very different, and the welding heat conduction difference is uneven, so that the good full penetration forming is not easy to effectively guarantee, and the workpiece is often deformed after welding, which affects installation. In order to figure out the mechanism of welding heat conduction of asymmetric welding on penetration and welding deformation, the influence of energy distribution and the size of heat input on the heat conduction is considered. The equivalent Gauss heat source model is introduced in the temperature field simulation, which effectively improves the calculation accuracy. The method of simulation and experiment was used to analyze the penetration formation, stress field distribution and welding deformation comparatively. The results show that when the welding current is the same and the welding torch angle is 20°, the welding deformation is larger and the deformation of the base metal is increased by about 18%. When the welding torch angle is constant, the welding deformation increases with the increase of the welding current, and the maximum deformation is 2.595 2 mm. The relevant research reveals the law of asymmetric weld penetration and welding deformation, which provides theoretical support for the optimization of welding quality and process parameters of this kind of asymmetric fillet welding.