The invention discloses an automatic assembly line for automobile seats and an assembly method. The automatic assembly line comprises a work table and conveying chains arranged on the two sides of the work table, and the work table is sequentially provided with a sliding rail set assembly station, a cushion set assembly station, a backrest set assembly station, a protection plate and safety belt buckle assembly station, a headrest assembly station, a wire arranging station, a first transferring station, a transitioning station, a second transferring station, an appearance function detection station, a repair station and a packaging station; a noise detection conveying work table located the side led to a sound insulation testing chamber is arranged on the side part of the first transferring station, and a noise detection outputting work table led to the second transferring station is arranged on the other side of the sound insulation testing chamber. According to the automatic assembly line, the labor intensity is lowered, the work efficiency is improved, the operation is orderly, errors and neglected assembly occur hardly, and the assembly quality of the seats can be guaranteed.