Butt welding tests were carried out on S355J2W+N weather-resistant steel by high-frequency pulse welding and ordinary pulse MAG welding respectively. By comparative analysis of the welded joint,the deep penetration root welding procedure,microstructure and mechanical properties of the joint were studied. The results show that,compared with ordinary pulse MAG welding,when the welding gap is "0",the high-frequency pulse MAG weld has a strong ability of root penetration,root weld width is increased by about 18.5%,in the case of smaller welding heat input（6.06 k J/cm）.Compared with ordinary pulse MAG welding,the microstructure characteristics of high-frequency pulse MAG welded joint are ideal,the more content of acicular ferrite（AF） at weld metal,none ferrite side plate（FSP） at weld metal and fusion zone,and the grain coarseness of the grain coarsened zone（CGZ） is less. The tensile strength of the butt-weled joint is greater than the lower limit of the base material strength,and the fracture position is located at the base material;when the bending angle of the bending sample reaches 180°,there is no crack on the tensile sample surface.Compared with the ordinary pulse MAG welding,the low temperature（-40 ℃） impact toughness of high frequency pulsed MAG welding joint is better,the impact energy of weld zone is about 9.6% higher than that of conventional pulsed MAG welding,and the impact energy of heat affected zone is about 12.3% higher.