The invention belongs to the technical field of automatic transmissions and particularly relates to an eight-gear automobile automatic transmission. The transmission solves the technical problems that in the prior art, adjacent planetary gears interfere with one other, an obtained transmission ratio depends on a presumed transmission ratio, and the limitation of the transmission ratio of a system is large. The transmission comprises a box, a power input shaft, three clutches, four brakes and a planetary gear system. The planetary gear system comprises a first sun gear, a second sun gear, a third sun gear, a first gear ring, a second gear ring, a first planetary gear with a step, a first planetary gear without a step and a planetary frame. The second sun gear, the third sun gear and the planetary frame are controlled by the first clutch, the second clutch and the third clutch respectively. The second sun gear, the first sun gear, the planetary frame and the second gear ring are controlled by the first brake, the second brake, the third brake and the fourth brake respectively. The transmission is easy to control, transmission efficiency of all gears is high, and the adjacent planetary gears do not interfere with one other.