The invention discloses a preparation method of a hydrogen-free compound modification layer on the surface of steel. The preparation method comprises the following steps of 1, pretreatment: performingpretreatment on the surface of a steel based workpiece; 2, inleakage of titanium: putting the steel based workpiece after pretreatment on a workpiece electrode carrying table of a vacuum chamber of double glow plasma surface alloying equipment, and performing inleakage of the titanium by taking a pure titanium plate as a source electrode and the steel based workpiece as a working electrode; and 3, carburization: after inleakage of the titanium is finished, changing the source electrode with high-purity graphite, performing carburization, stopping heating the steel based workpiece after carburization is finished, performing deposition on the steel based workpiece for 1-100min to form a carbon deposition layer, and forming the hydrogen-free compound modification layer on the surface of thesteel based workpiece finally. According to the preparation method provided by the invention, the the hydrogen-free compound modification layer which is composed of hydrogen-free titanium carbide, ferrite, carbide and free carbon is prepared on the surface of the steel based workpiece, and the hydrogen-free compound modification layer has the effects of wear resistance and reduction; and the method is environmentally friendly, can be realized by one double glow plasma surface alloying equipment and is high in reliability and low in preparation cost.