Abstract: Applying the principle of Step Acceleration Method(Pattern Search Method), two parameter values of double ellipsoid heat source model, the rear half of semi-axe Cr and the front half of semi-axe Cf, can be predicted by the combination of finite element numerical simulation and temperature measurement in X70 steel during multiple wires submerged arc welding.The result illustrated that the temperature field curve obtained by numerical simulation was very similar with the one obtained by the experimental measurement, with the global error e only 0.615 8 in the weld region(the front surface region 10 mm far from weld center line and the back region 14 mm far from the weld center line)when C_ri equal 15, 20, 30 millimeters and C_fi equal 6, 6, 8 millimeters(i=1, 2, 3), which demonstrated the rationality and accuracy of the value of two types of parameters of the double ellipsoid heat source model in the multiple submerged arc welding by using Step Acceleration Method.