Abstract: A new modeling method of weld bead profile by MAG welding process was proposed and the edge of the profile was extracted based on wavelet transform.The different interpolation methods, the cubic spline, the constrained cubic spline and the B-spline curve, were utilized respectively, the cross-section edge of weld bead was fitted by least square method, and then the mathematical model of the profile was achieved.The experimental results show that the method is effective to detect the cross-section outline of the profile, the constrained cubic interpolation is preferred choice to interpolate the data of the profile, and the cross-section profile mathematical model of weld bead is sine curve under our experiments.