An electric curtain device comprises a rail assembly and a driving assembly, the rail assembly comprises a rail body, a transmission belt, a transmission rod, a pulley, a linkage piece, a hook and a locking supporting piece, and the locking supporting piece is installed in the middle or at the end of a sliding groove body, prevents the pulley from passing through and supports the transmission rod, the two pulleys in the middle are respectively connected with two different side edges of the transmission belt through connecting pieces; the driving assembly is arranged at the end, close to the driving belt wheel, of the track body and comprises an opening and closing driving component and a dimming driving component, the opening and closing motor assembly is parallel to the track body, the dimming motor assembly is perpendicular to the track body, and the whole opening and closing transmission gear set is located over the dimming driving component. Opening, closing and dimming of the curtain can be independently controlled, transmission of the whole driving assembly is efficient, the structure is small, a user can flexibly lock the supporting piece, and installation is convenient; and the transmission rod connected internally enhances the rigidity, so that the requirement of a large-breadth curtain is met, and the whole device is low in operation noise.