A method for preparing active carbon-based special synthetic paper capable of degrading harmful substances in environment, including: stirring polyurethane particles and a solvent in a reactor, and standing to completely dissolve the polyurethane particles to obtain a polyurethane solution; adding active carbon having harmful substances adsorption property in the obtained polyurethane solution, stirring and mixing uniformly to obtain a solid-liquid mixture; coating the obtained solid-liquid mixture onto a piece of release paper, soaking the release paper coated with the solid-liquid mixture into an aqueous solution of silver nitrate having photocatalytic degradation property, completely curing the solid-liquid mixture to form a film, and soaking the release paper and the film into an aqueous solution of sodium chloride; drying the obtained release paper and the film in an electric blast drying oven, and stripping the film from the release paper to obtain the active carbon-based special synthetic paper.