A method of adhering multiple polyurethane foam layers together sticks a first polyurethane foam layer with a second polyurethane foam layer by using polyurethane system components in polymerization foaming reaction. The method contains steps of: A. delivering the first polyurethane foam layer toward a cladding position; B. cladding or depositing the polyurethane system components on the first polyurethane foam layer at the cladding position so that the polyurethane system components start foaming polymerization on and adhere with the first polyurethane foam layer; C. delivering the polyurethane system components and the first polyurethane foam layer to a press roller so that the polyurethane system components foam to produce the second polyurethane foam layer, and the second polyurethane foam layer adheres with the first polyurethane foam layer; and D. conveying the second polyurethane foam layer and the first polyurethane foam layer away from the press roller.