The invention belongs to the technical field of semiconductor materials, and particularly relates to a preparation method of a graphene and tin oxide hollow sphere composite nanomaterial, wherein themethod comprises the steps: adding deionized water into K2SnO3.3H2O, mixing urea with an ethanol solution, combining a potassium sulfate aqueous solution and a urea solution, and carrying out ultrasonic treatment to form a mixed solution; dispersing graphene oxide into water, adding the mixed solution, uniformly stirring, transferring into a high-pressure stainless steel reaction kettle taking polytetrafluoroethylene as a lining, putting the reaction kettle into a vacuum drying oven, and carrying out reaction; and after the reaction is finished, rapidly putting the high-pressure reaction kettle into ice water to quench, washing the cooled liquid with deionized water and absolute ethyl alcohol respectively, and performing vacuum drying to obtain the G/SnO2 hollow sphere composite nanomaterial. The third-order nonlinear absorption of the G/SnO2 hollow sphere composite nanomaterial synthesized by the method is saturated absorption, the third-order nonlinear refraction is self-focusing, and the G/SnO2 hollow sphere composite nanomaterial is expected to be applied to a mode-locked pulse laser, an optical memory, an optical modulator and the like.