The S-N equation is one of the most important equations in fatigue model
investigation. A majority of fatigue models, including multiaxial
fatigue model and mean effect models, are established on the basis of
the S-N equation. Obviously, an accuracy of the S-N equation is very
important. Taking into account that the S-N equation is, in fact, an
empirical one in which the material constants are determined by
numerical fitting fatigue experimental data, in this paper, the S-N
equation can be improved, by further processing these fatigue
experimental data, to present a new type of S-N equation that is more
accurate than the S-N equation. The new type of S-N equation is called a
similar S-N equation in this paper. By using a large number of
experimental data of metallic materials reported in literature, an
accuracy of the similar S-N equation has been proven.