A method of joint control of seam tracking and welding quality was proposed by using an ultrasonic sensor for measuring welding penetration and electric arc sensor for seam tracking. The electric arc sensor was gotten of the welding deviation information and ultrasonic sensor was gotten of the welding penetration information. Then transformed the gotten penetration information to deviation information, using the fusion algorithm of combination of optimal weight and recursive least square algorithm to process deviation information of seam tracking gotten by the two sensors, the accuracy of seam tracking could be improved effectively. By inputing the fused seam tracking information and welding penetration information into fuzzy controller with threeinput and twooutput, inspecting the welding quality online is realized, improving accuracy of seam tracking at the same time.