Abstract: Double ellipsoid heat source model is often used in numerical simulation of high energy beam welding.The precision and efficiency of computation are greatly influenced by the shape parameters of model.Due to lack of quantitative formula,the shape parameters have to be obtained by repeating tentative calculations by experience before.And the tentative calculation is affected by random factors to a great extent.Therefore an algorithm is presented so that the shape parameters can be calculated by empiric formula,also the algorithm is verified as valid by FEM computation.It indicates that parameters needed in simulation can be easily obtained by simple analytical calculation.By using this algorithm,the tentative calculations can be omitted,and the efficiency and precision of computation can be improved greatly.