The invention discloses nitrogen-doped carbon flexible paper and a preparing method and application thereof. Melamine foam is subjected to low-temperature thermal oxidation in the air and then to high-temperature thermal treatment in the presence of inert gases under the action of mechanical pressure, so that the nitrogen-doped carbon flexible paper is obtained. Low-temperature thermal treatment is conducted on the melamine foam firstly to introduce a small number of oxygen-containing functional groups into the melamine foam, so that cyclization of the melamine foam is promoted during high-temperature thermal treatment, the nitrogen-doped carbon paper can have high buckling flexibility, the thickness, density and conductivity of the nitrogen-doped carbon flexible paper are regulated within the flexibility range, flexibility is high, and large-scale production can be achieved easily. The prepared flexible paper has connected carbon network structures, has high buckling flexibility, and can be bent freely. The flexible paper has high oxygen reduction catalytic performance. The prepared nitrogen-doped carbon flexible paper can be used as a self-supporting flexible electrode material of a flexible electric device.