The invention relates to a dual clutch type variable transmission device with a planetary gear train. The device consists of a sun axle, a first countershaft, a second countershaft, an intermediate shaft, dual clutches, a synchronizer, a gear and a planetary gear train, by the combination of the planetary gear train, the dual clutches, the synchronizer and the gear, automatic smooth gear shifting can be realized; and by a structure of the planetary gear train and the sharing gear, the gear number is greatly increased, and the number of shift gears can be reduced. Each pair of gears has less small speed ratio and is in a short transmission shaft structure, so the rigidness of a speed changer is improved, and the radial and axial sizes of the speed changer are reduced; a cylindrical gear is used for replacing a conical gear, so a differential mechanism has a compact structure, the manufacture cost of the differential mechanism is reduced, the gear axial pressure of the conical gear differential mechanism is eliminated, and the transmission efficiency of the differential mechanism is improved.