The invention relates to a manganese dioxide/carbon paper composite electrode material and a preparation method thereof, belonging to the technical field of a super-capacitor electrode material. The material adopts carbon paper as a matrix (a current collector), a manganese dioxide nano sheet is attached to the surface of the carbon paper, the length of the manganese dioxide nano sheet is 150 to 200 nm, and the thickness of the manganese dioxide nano sheet is 5 to 15 nm. The preparation method comprises the following steps of: firstly sufficiently and uniformly mixing potassium permanganate, ammonium fluoride and deionized water according to a given ratio to obtain a mixed system, immersing the carbon paper in the mixed system, performing the reaction, and finally washing and drying a reaction product. The preparation method is simple, rapid and capable of realizing the mass production; the obtained composition material is controllable in size, regular in shape, good in electrochemical performance, particularly high in capacitance and good in cycling performance, the solves the technical problems of the prior art that the structure is unstable and the multiplying power performance is poor, and is particularly suitable for a super-capacitor material; in addition, the composite material can also be applied to a flexible device.