The invention provides a device for automatically assembling an engine sealing ring. The device comprises a feeding mechanism, a picking mechanism and an assembling mechanism; the feeding mechanism is used for positioning the position of a sealing ring through a positioning shaft and a clamping jaw; the picking mechanism is accurately positioned through a round shaft and a hole in the front end of the feeding mechanism and is used for accurately picking one sealing ring through a picking clamping jaw and a secondary jaw block; after picking, the picking mechanism automatically feeds to the assembling mechanism, and the picking clamping jaw and the clamping jaw of the sealing ring are matched with each other to feed twice. According to the device, the position of an opening of the sealing ring is adjusted by the assembling mechanism through a photoelectric sensor, a sealing ring sleeve, a flange and a servo motor; the sealing ring sleeve, the flange, a cylinder and the sealing ring clamping jaw are matched with each other to adjust the axial position; the sealing ring clamping jaw, a sealing ring compressing plate and a pushing block are used for assembling the sealing ring to a cam shaft.