The invention discloses polyolefin lithium battery diaphragm coating slurry, which is prepared by a coating material, a binder and deionized water, wherein the coating material is composed of one or more of graphene coated Al2O3 powder, carbon nanotubes, graphene and graphite according to any proportion; the binder is composed of one or two of sodium alginate, carboxymethylcellulose sodium, styrene butadiene rubber and polyvinylidene fluoride according to any proportion; the mass ratio of the coating material and the binder is 10:(0.01-1), the balance is the deionized water, and the mass fraction of the coating material in the polyolefin lithium battery diaphragm coating slurry is 0.1-30%. The invention further discloses a method of coating a polyolefin lithium battery diaphragm by using the polyolefin lithium battery diaphragm coating slurry. The coating slurry takes water as a solvent, and has the advantages of low cost, environment friendliness, controllable viscosity of the coatingslurry and good wettability and dispersion of the coating slurry. The method of the invention is simple in preparation process, low in cost and suitable for large-scale production.