The invention relates to a preparation method of nitrogen-doped porous carbon, and in particular relates to a method for preparing doped porous carbon by taking a heavy organism as a carbon source, belonging to the technical field of carbon material preparation. The method comprises the following steps of: firstly, conducting a reaction between a nitrogen source and formaldehyde to generate a prepolymer; then, mixing the prepolymer with a template and the carbon source, and reacting at certain temperature; and finally, curing and carbonizing a crosslinking product to obtain nitrogen-doped porous carbon. The method provided by the invention can obtain nitrogen-doped porous carbon with different pore structures and nitrogen contents through multiple ways such as control on the nitrogen source type, temperature control, control on the mass ratio of a carbon source to a nitrogen source, control on the dosage of a template agent and the like. By adopting a chemical polymerization blending carbonization method, the method effectively controls the loss of nitrogen in a thermal treatment process and improves the utilization rate of the nitrogen source; the selection range of the raw material is wide; and the method is easy to operate and easily realizes large-scale preparation while providing a new way for efficiently utilizing heavy organic matters.