Abstract: The Saturation Level of Carbon (A) is defined as Cs/Cp.Cs-carbon content of steel; Cp-a parameter of carbon in proportion to the contents of carbide forming elements in steel, presented by G.Steven^[2].The relationship between three factors are established in this paper, i.e. saturation level of carbon (A), quenching temperature (T_Q) and secondary hardness (HRC_T).This work confirms that the value of A can be used as a composition parameter to evaluate the secondary hardening ability of steel, and that A can also be used to choice the quenching temperature of individual heat for certain object of selected secondary hardness. Furthermore, the influence of several alloying elements on secondary hardening ability of steels containing W12, Mo3, Cr4 and V3 had been investigated, and the interchange ability between elements in high speed steel had also been discussed.