The invention relates to a method of preparing base oil of lubricating oil from raw materials with a high wax content. The method comprises the following steps: at first, mixing a pretreatment solution with an isomerization de-waxing catalyst and preprocessing the isomerization de-waxing catalyst so as to obtain a preprocessed isomerization de-waxing catalyst; then adding the obtained preprocessed isomerization de-waxing catalyst into a reactor, carrying out hydrogen activation; finally contacting raw material oil and hydrogen gas with the activated isomerization de-waxing catalyst and carrying out isomerization de-waxing reactions in an atmosphere of hydrogen sulfide with a certain concentration. Through inhibiting the cracking activity of the isomerization de-waxing catalyst in the primary stage of reactions after hydrogen activation, the isomerization selectivity of the isomerization de-waxing catalyst can be improved, and thus the yield of base oil of lubricating oil is increased.