The invention discloses a method for synthesizing a NaxMnO2 cathode material of a sodium-ion battery. The method comprises the following steps: 1) adding a sodium salt, a manganous salt and polyvinylpyrrolidone into water, stirring for mixing, and drying so as to obtain dry gel; 2) heating the dry gel obtained in the step 1) until being combusted, and further calcining the product obtained after combustion, so as to obtain the NaxMnO2 cathode material. The method for synthesizing the NaxMnO2 cathode material of the sodium-ion battery, which is disclosed by the invention, is a macromolecule gel-combustion synthesis method, polyvinylpyrrolidone is adopted as a chelating agent and fuel, sodium and manganese can be fixed on macromolecule chains in a chelation manner, uniform mixing of molecule levels can be achieved, and the electrochemical property of the product can be greatly improved; the prepared NaxMnO2 cathode material is very excellent in power magnification and circulation property; the method is simple in process, convenient to operate, simple in equipment, easy in automation control, low in cost and applicable to large-scale industrial production.