The base solution of poly(p-phenylenediamine)(PPTA) was prepared using p-phenylenediamine and p-phenylenediamine chloride as raw materials, and the coating solution containing alumina powder was made. It was coated on the polyethylene(PE) separator. The effects of PPTA with different characteristic viscosities on the appearance of the coating layer, the influence of moisture content on the polymerization reaction, the influence of the mass fraction of alumina powder on the Gurly value of PE separator were studied. The results show that when the intrinsic viscosity of PPTA for coating is about 2.0 dL/g, a coating layer with a good surface effect can be obtained. When preparing the PPTA base solution, controlling the water content of the system at about 0.05% is conducive to the stable preparation of the PPTA stock solution with an intrinsic viscosity of about 2.0 dL/g. When the mass fraction of alumina in the PPTA coating layer is around 60%, a coating layer with a lower Gurly value can be obtained.