Using two welding processes,high-frequency pulse MAG welding and conventional pulse MAG welding,the welding process test was carried out on the 12 mm thick SMA490BW weather-resistant steel plate T-joint（fillet weld）,the macroscopic,penetration and the microstructure of the welded joint were analyzed,and the Vickers hardness HV10 and welding residual stress of the welded joint were also tested. The results show that comparing to the ordinary pulse MAG welding at the similar welding heat input value,the penetration of highfrequency pulse MAG welding increases by 20% ～30%,the residual stress at the HAZ（12 mm from weld toe） reduces by about 11%～26%,the high-frequency pulse MAG welded joint shows ideal microstructure characteristics,there is high content of acicular ferrite（AF） in weld,no ferrite side plate（FSP） and less content of grain boundary ferrite（GBF） in bond,and the grain coarseness of the grain coarsened zone（CGZ） is less. The vickers hardness HV10 value of the welded joint in two welding processes is less than 380 HV10,which meets the requirements of the welding procedure qualification standard.