The present invention belongs to the field of mechanical automatic speed variator for vehicle, and is especially one kind of double clutch type automatic gear box in new structure. The automatic gear box includes various setting gear pairs, synchronous shifting unit and shifting control system, and features that each of the power input shaft and the power output shaft is provided with one wet clutch, all the setting gear pairs are divided into odd number set and even number set connected separately to the driven sheet of one of the clutches, and two clutches transmit the work power alternately to realize setting switching. The shift process has no power interruption, short shifting time, greatly raised shifting comfort and excellent shifting power performance and quality of vehicle. The present invention has simple and compact parallel shaft structure, low cost but the same effect as automatic rotary shaft gear box in complicated structure.