The invention discloses a preparation method of a steel rod of a rod mill, belonging to the field of wear-resistant materials. The steel rod of the rod mill comprises the following components in percentage by mass: 0.6-0.85% of C, 0.17-0.37% of Si, 0.7-1.2% of Mn, less than or equal to 0.035% of P, less than or equal to 0.035% of S, less than or equal to 0.6% of Cr and 0.01-0.02% of Nb. The preparation method of a grinding rod comprises the steps of smelting, continuously casting a round billet, and rolling round steel with the diameter of 50-120mm and the fixed length of 2-7m by using a TMCP (Thermal Mechanical Controlled Process); directly quenching in water for 5-10min by utilizing waste heat after rolling; then, tempering at low temperature. The method can be used for obtaining the grinding rod which has gradient hardness, the surface hardness of HRC60 and the core hardness of HB200 and the steel rod which is high in surface hardness, good in wear resistance, relatively high in core toughness and favorable in matching between hardness and toughness. The method disclosed by the invention is simple in process, high in efficiency, low in energy consumption, low in cost and capable of realizing actual industrial production and application.