Abstract: The effects of alkyl-naphthalene which is one of the pour point depressants (PPD) on the amount of wax precipitated from the simulation oil are studied in this work.The amount of wax precipitated at different temperature is measured with a high speed centrifuge which can separate precipitated wax from oil under a specific temperature. Carbon number distributions and composition of simulation oil, PPD and the oil added with PPD are measured with gas chromatography. According to the experiments, the results indicate that the amount of wax precipitated at different temperatures decreases, the tendency of reduction is nearly consistent when the concentration of PPD is 0.2% and 0.5%; while with l%, the carbon number distributions of precipitated wax that are different from the primary wax show double apices; PPD restrains the deposition of hydrocarbon of small carbon number in the simulation oil, while promotes the deposition of hydrocarbon of large carbon number.