K-TIG is a welding process based on traditional TIG welding, which increases the welding current to 300 A or even higher value and forms the“keyhole”effect by the feat of tungsten electrode cooling system to achieve the ultimate deep penetration welding. The welding width of K-TIG welding is wider than that of plasma and laser weld, and the weld pool is larger. The traditional heat source model is not suitable for the characteristics of heat source distribution in K-TIG weld. Based on the SYSWELD simulation platform and the experimental results of K-TIG welding for titanium alloy, a combined heat source model for numerical simulation of K-TIG deep penetration welding of titanium alloy was developed. The results show that when the distribution coefficient of double ellipsoidal heat source is 0.75 and the acting depth is 4 mm, the simulation weld pool is consistent with the actual joint cross section, and the front weld width is 12 mm and the back weld width is 5 mm. The finite element simulation results of temperature loop curve and residual stress are basically consistent with the experimental results, verifying the accuracy of the established K-TIG heat source model.