A traditional copolymer pour point depressant PSMS was prepared by radical polymerization of stearyl acrylate, maleic anhydride and styrene monomers with azobisisobutyronitrile as initiator. In order to improve the pour point depressant effect and stability of the polymer, the organically modified montmorillonite (OMMT) and the polymer pour point depressant PSMS were selected for solution intercalation and composite to prepare the nanocomposite pour point depressant PSMS/OMMT. It was applied to Karamay crude oil for effect evaluation, and the mechanism of pour point depressurization was preliminarily elucidated with the help of Polarizing microscope (POM) and other tests. Studies have shown that the addition of 10% (based on monomer quality) of modified montmorillonite and the use of 0.1%(based on crude oil quality) of PSMS/OMMT can reduce the pour point of Karamay crude oil by 25 °C, and the viscosity reduction rate reaches 65.7%; compared with pure polymer pour point depressant, the usage is reduced by 1/3, the pour point decreased by 3°C, the viscosity reduction rate is increased by about 10%, and anti-aging performance has also been greatly improved.