Based on the welding procedure of butt downhand welding of double-sided asymmetric groove with arc welding robot,the influence of welding current and welding speed on welding quality is studied by experiment. The results show that for 20 mm asymmetric double groove,with the backing welding parameters of current of 170 A and welding speed of 0.25 m/min,the appearance of weld is good,the filling height is suitable,and the back weld root is well formed. When using pulse MAG welding with current of 245 A and welding speed of 0.25 m/min,the back weld root is completely pene-trated,no hardened structure appears in the heat affected zone,and the molten width of truncated edge increases from 3 mm for MAG welding to 5 mm for pulsed MAG welding. This solves the technical problem that the welding automation application is difficult to realize without back chipping in the hydropower hydraulic steel structure industry.