The present invention relates to a high-strength spring steel and its manufacturing process. More specifically, it relates to a high-strength spring steel characterized in that it is obtained by heating the surface of the material steel to over the AC.sub.3 transformation point by the high-frequency induction heating or the like, stopping the heating and then decreasing the surface temperature of said material steel to below the Ar.sub.1 transformation point, this short-time heating of the surface being repeated to secure heating throughout the entire steel body or a condition close to it, under which the steel is quenched, whereby the crystal grains in the steel become increasingly finer from the core to the surface layer of the steel, the crystal grain size of the metal in the surface layer being extraordinarily fine; the invention also relates to the process of manufacturing the steel.