Abstract: Two new equations of the S N curve equation and the E N curve equation are presented in this paper. These equations are with four parameters, therefore they have better physical properties than those with two or three parameters. By means of the optimization method of correlation coefficient the parameter estimation formulas and numerical solutions of these equations are established. Finally, two examples of these equations application are given. From these examples, iTis shown that the equations are not only of excellent fitting effect, but also convenient for application.