The invention provides a preparation method of a sodium titanate / graphene composite cathode material of a sodium ion battery, which is used for solving the problems in the prior art that no sodium ion battery cathode material with excellent comprehensive performance is provided, and belongs to the field of sodium ion secondary batteries. The method comprises the steps of dispersing graphene oxide to obtain a graphene oxide solution, mixing the graphene oxide solution, a sodium-containing compound and a titanium-containing compound, carrying out reaction to obtain a composite precursor, mixing the composite precursor with a binder, carrying out atomizing drying and granulating to obtain a spherical composite precursor, and finally burning the spherical composite precursor in an inert atmosphere to obtain a micro-scale spherical sodium titanate / graphene composite cathode material. The composite cathode material has the advantages of high sodium storage capacity, long cycle life, good large-current discharge property, high compaction density and the like, and the requirement of the high-performance sodium ion battery for the comprehensive performance of the cathode material can be met.