Abstract: The invention relates to a method for the preparation of the polyolefinic bases of synthetic oils by the cationic oligomerization of olefinic feedstock and can be used in the petrochemical industry. A new method for the preparation of the polyolefinic bases of synthetic oils has been developed, which comprises the steps of conditioning olefinic feedstock, preparing and dosing in a reactor, solutions and suspension of the components of a catalytic system Al(O)—HCl-TBCh, isomerizing alpha-olefins and oligomerizing higher olefins and mixtures thereof under the action of the catalytic system Al(O)—HCl-TBCh, separating spent catalyst, dividing an oligomerizate into fractions and hydrogenating the fractions separated under the action of a catalyst Pd(0.2% w)/A1203+NaOH. The invention provides the improvement of all steps of the method elaborated.