The invention relates to a dedicated automatic transmission planetary gear mechanism of pure electric vehicles. The mechanism comprises a gear ring, a front planetary gear engaged with the gear ring is sleeved on one end of a planet carrier, and a rear planetary gear is sleeved on the planet carrier as well; a front central gear engaged with the front planetary gear is arranged on one end of a gear shaft, and is positioned in the gear ring; the gear shaft is an input shaft one end of which is inserted in an output shaft through a bearing, and the output shaft is provided with a rear central gear which is engaged with the rear planetary gear; the other end of the gear shaft is connected with one end of the planet carrier through a three-gear clutch C, and the planet carrier is provided with a forward-gear one-way clutch (F1) and a reverse-gear brake (B); and the outer side of the gear ring is connected with a one-way clutch F2. The efficiency of the mechanism is higher than the efficiency of an automatic transmission with the planetary gear mechanism of the fuel vehicle; and the mechanism has the advantages of simple gear arrangement structure, compact structure, small size and light weight, which accord with the principle of the lightweight design of vehicles.