Abstract: For the problem that the uniform welding speed leads to bad shape at the peak of fillet weld seam during tracking the large fillet weld seam of mobile welding robots,the method of welding current adjusted on-line and in time according to the welding speed is presented.First,Kinematic analysis of the large fillet weld seam tracking is given,and the welding speed is changed follow cosine law to achieve the normal welding.Then,welding current is adjusted on-line according to the changes of welding speed in welding process.Welding current matched to welding speed is gained by experiments.By matching experiments,welding current at the fillet position matched to the average value of welding speed is obtained.The experiment results of 90 angle degree fillet welding seam tracking indicate that the method can improve welding quality at the peak of fillet weld seam effectively.