A modified conjugate method for unconstrained optimization problem was presented on the basis of DY conjugate gradient method.It is proved that the new formula is of full descent under the condition of the strong wolfe line search. At the same time ,the new formula can support the global convergence.The numerical results show that the method is of great value. And the algorithm was applied to nonlinear parameter estimation of buring anteisodynamics model of sulfur dioxide acted on by caesiumrubidiumvaradium low temperature sulfur acid catalyst, and oblaine satisfactory results were obtained.