The invention discloses an automatic transmission which comprises a first shaft system, a second shaft system, three positive gear groups, three planetary gear groups, four clutches and two brakes, wherein the first shaft system and the second shaft system are arranged in the same transmission box body side by side, the first shaft system is positioned on the drive side, and the second shaft system is positioned on the driven side; the two shaft systems are connected with each other through a plurality of power paths to which the three positive gear groups belong. At least nine forward gear positions and at least one reverse gear position are realized by only using six gear position shifting units, and the inter-gear-position ratio of the common gear positions is ranged from 1.091 to 1.297; the total drive ratio is up to 8.016; gear position shifting is smooth, and the structure is kept compact; the running dynamic performance of a vehicle is improved, and the oil consumption is further reduced; the automatic transmission is economical, and the environment can be protected favorably. The automatic transmission is suitable for hybrid driving and has a function of automatically starting and stopping an engine.