The main objective of this study is to generate new understanding and improve computational method for optimization design on the parameters of double ellipsoid welding heat source. On the basis of Infrared measurement (IR), two optimization design methods, the zero-order method and first-order method, were combined to confirm the heat source parameters. The simulated thermal cycles, the weld penetration and the weld width were consistent to the experimental results with such corrected parameters. The effects of the parameters were analyzed by gradient evaluation method. It presents that as each of the parameters increasing, the peak temperature in the thermal cycle declines. Of all the three parameters, the sensitivities of the weld penetration and width with parameter c are great.