The invention discloses an O-shaped ring assembling device which comprises a turntable device, a first feeding device, a first detection sensor, a second feeding device, a second detection sensor and a discharging device. When the O-shaped ring assembling device is in operation, only one operator is needed to perform related assisting, and the operator firstly puts an O-shaped ring workpiece to be assembled on an assembly station of a turntable working table. After the device is started, the first feeding device, the first detection sensor, the second feeding device, the second detection sensor, an intelligent camera detection device and the discharging device which are arranged around the turntable device perform automatic matched operation, a first O-shaped ring and a second O-shaped ring are quickly and accurately assembled on the workpiece, and accepted product and defective product classification and output are performed, so that the O-shaped ring assembling device is simple in operation, high in production efficiency and capable of achieving automatic operation to the most extent and greatly saving labor.