An electric rotation device for an automobile seat, the device comprising: a rotary support; a rotary disc, located under the rotary support and fixedly connected to the rotary support and a seat cushion frame in a seat; a fixed disc, located under the rotary disc and connected to an upper slide rail in a slide rail assembly of the seat; a platen, located above the rotary disc and under the rotary support and fixedly connected to the fixed disc; an upper ball assembly, located between the platen and the rotary disc, an upper ball in the upper ball assembly being configured for rolling contact with the platen and the rotary disc; a lower ball assembly, located between the rotary disc and the fixed disc, a lower ball in the lower ball assembly being configured for rolling contact with the rotary disc and the fixed disc; and a driving motor assembly, mounted to the fixed disc and comprising: a driving gear; and a semicircular rack, mounted to the rotary support, a center of circle of the semicircular rack coinciding with a center of rotation of the rotary support, the semicircular rack being meshed with the driving gear, and the driving gear in the driving motor assembly being configured to drive, by using the semicircular rack, the rotary support to perform reciprocating rotation in a range of 0-180°, characterized in that special-shaped teeth (860, 870) configured to prevent the driving gear from rotating out of the semicircular rack are respectively disposed at each of extreme positions on two ends of teeth in the semicircular rack, so that the driving gear is gradually snapped with the special-shaped teeth (860, 870) to stop further rotation when rotating to the extreme positions on the two ends of the semicircular rack. a rotary support; a rotary disc, located under the rotary support and fixedly connected to the rotary support and a seat cushion frame in a seat; a fixed disc, located under the rotary disc and connected to an upper slide rail in a slide rail assembly of the seat; a platen, located above the rotary disc and under the rotary support and fixedly connected to the fixed disc; an upper ball assembly, located between the platen and the rotary disc, an upper ball in the upper ball assembly being configured for rolling contact with the platen and the rotary disc; a lower ball assembly, located between the rotary disc and the fixed disc, a lower ball in the lower ball assembly being configured for rolling contact with the rotary disc and the fixed disc; and a driving motor assembly, mounted to the fixed disc and comprising: a driving gear; and a semicircular rack, mounted to the rotary support, a center of circle of the semicircular rack coinciding with a center of rotation of the rotary support, the semicircular rack being meshed with the driving gear, and the driving gear in the driving motor assembly being configured to drive, by using the semicircular rack, the rotary support to perform reciprocating rotation in a range of 0-180°, characterized in that special-shaped teeth (860, 870) configured to prevent the driving gear from rotating out of the semicircular rack are respectively disposed at each of extreme positions on two ends of teeth in the semicircular rack, so that the driving gear is gradually snapped with the special-shaped teeth (860, 870) to stop further rotation when rotating to the extreme positions on the two ends of the semicircular rack. a driving gear; and a semicircular rack, mounted to the rotary support, a center of circle of the semicircular rack coinciding with a center of rotation of the rotary support, the semicircular rack being meshed with the driving gear, and the driving gear in the driving motor assembly being configured to drive, by using the semicircular rack, the rotary support to perform reciprocating rotation in a range of 0-180°, characterized in that special-shaped teeth (860, 870) configured to prevent the driving gear from rotating out of the semicircular rack are respectively disposed at each of extreme positions on two ends of teeth in the semicircular rack, so that the driving gear is gradually snapped with the special-shaped teeth (860, 870) to stop further rotation when rotating to the extreme positions on the two ends of the semicircular rack.