Abstract: During the direct computation of vP/vS by ray-path elastic impedance,the analytic expression is high-power function consisted of the ratio of two elastic impedance,which has poor stability and anti-noise ability,so it is limited for application.Therefore,one modified ray-path elastic impedance need to be developed to make the computation of elastic parameters more stable.Through using binomial theorem quadratic to the ray-path elastic impedance formula,the ray-path elastic impedance was expressed into a function of P-wave impedance and S-wave impedance.By experimental analysis and error derivation,analytical formula of P-wave impendence,S-wave impendence and other elastic parameters were given.The application in some offshore area obtained good results.