An object of the disclosure is to provide a method of efficiently producing a highly-pure vanadium electrolytic solution from a combustion residue that is discharged from facilities such as refineries and power plants and contains uncombusted carbon. The method of producing a vanadium electrolytic solution for redox flow cell (RFB) includes a vanadium eluate generation step of obtaining a vanadium eluate in which vanadium is dissolved. The vanadium is contained in a combustion residue obtained after combustion of a fossil fuel. The method further includes a precipitation step of mixing a sulfide precipitant into the vanadium eluate to precipitate a solid substance of precipitate in a reduction state and a wet oxidation step including a process of adding dilute sulfuric acid to the solid substance separated from the solution to generate a vanadium sulfate solution.