The invention discloses a transformable three-carriage sedan car and relates to a trunk transformation technology of a common three-carriage sedan car. The transformable three-carriage sedan car consists of a car roof, car body side walls, a rear car window, an arch frame, a trunk, a trunk side wall and a trunk cover, and is characterized in that: the upper part of the rear car window is hinged with the car roof; the lower part of the rear car window is connected with the trunk cover through the arch frame; locking devices are symmetrically mounted at the two ends of the inner side of the lower part of the rear car window; a lifting glass window is mounted in the trunk side wall; a sealing plate lifting device is mounted at the tail part of the trunk; and sealing devices are mounted in the connecting positions of the car roof, the car body side walls, the trunk side wall, the trunk, the rear car window and the trunk cover. the transformable three-carriage sedan car has the characteristics of novelty in structure, convenience in transformation, low cost, safety, reliability, good economy, attractive appearance and excellent comfort, and is a novel transformable three-carriage sedan car with the integration of economy and practicality.