The invention relates to a method for assembling railway passenger car modular floors. The method comprises the following steps: assembling a floor reference module and a floor interoperation module outside a passenger car; treating the ground of the passenger car; assembling the floor reference module; and assembling the floor interoperation module and the like. The method can effectively reducethe number of parts and components assembled on the car to ensure an orderly production environment, can improve the product quality and the production efficiency, reduce the labor intensity of workers, and finally shorten the manufacture period of the vehicle.