Abstract: This work contains two parts:(1)A charge curve equation having no appro_ximation for passivated metal corrosion systems is derived and compared with the routine charge curve equation,which is virtual only when the polarization is minim(linear range)(2)It is simpler to analyze charge curve data by from of charge differential equation than from charge curve equation.After the charge curve data are measured,the slope of charge curve is computed by numerical differentiation method,then the charge differential equation may be transformed to a set of linear equations using polynomial approximation.The electrochemical parameters of corrosion system would be calculated out from this set of linear equations using regression analysis.The advantage of this method is that there is no restriction of "linear range" and corrosion current density may be gained directly.