The invention relates to a preparation method of cellulose spinning dope for carbon fibers. The preparation method comprises the following steps of: (1) crushing graphene oxide, adding the crushed graphene oxide to a solvent, and stirring and applying ultrasound to the graphene oxide and the solvent to obtain dispersion liquid of the graphene oxide, wherein the mass fraction of the dispersion liquid of the graphene oxide ranges from 0.01% to 10%; and (2) dissolving sodium hydroxide in the obtained solution, adding cellulose to the solution at minus 10 to minus 5 DEG C, stirring and dissolving the cellulose, and defoaming the solution to obtain the cellulose spinning dope for the carbon fibers, wherein the mass ratio of the graphene oxide to the cellulose is 0.01:100 to 15:100. The preparation method is simple in process, can effectively improve the degree of orientation of molecules of the cellulose and improve final carbon yield in a spinning process on the premise of maintaining the original characteristics of the cellulose, is beneficial to improving strength and modulus, and can be used for preparing the high-performance carbon fibers with the cellulose.