Abstract: Polyethylnaphthalenes lubricating base oil were synthesized by alkylation of cooking naphthalene with ethylene using organic ammonium salt/metal chloride ionic liquid as catalyst. It was found that the AlCl₃/Et₃NHCl ionic liquid showed better active in the naphthalene alkylation with ethylene by regulating the composition of anions and cations in ionic liquids. Two different compositions of polyethylnaphthalenes base oils PEN-1 (92.9% of mono- and di-ethylnaphthalenes) and PEN-2 (91.3% of polyethylnaphthalenes) were synthesized by optimizing reaction conditions (catalyst dosage, reaction time and temperature). The lubrication test results showed that PEN-2 base oil with a large number of alkyl side chains exhibited good tribological properties and showed better wear resistance than the commercial alkylnaphthalenes base oil AN5, showing a good application prospect.