The invention discloses an automatic speed-changing device for an electric automobile, which is characterized by being provided with a layout form, wherein in the layout form, the whole structure is two parallel shafts, one shaft is an input shaft and the other shaft is an output shaft; and the input shaft is distributed with two groups of inner planetary gear mechanisms and outer planetary gear mechanisms which form an inner and outer wrapping relation. The automatic speed-changing device controls the inner planetary gear mechanisms and outer planetary gear mechanisms to realize speed change by the combination of connection and disconnection of different electromagnetic clutches and electromagnetic brakes on the input shaft and the output shaft, an electric control mode thereof is more suitable for being applied in the electric automobile, six output states with different rotating speeds can be realized, the power of a motor can be effectively reduced, the ranges of the rotating speed and the torque force of the electric vehicle can be expanded, and the power and passing performance of the electric vehicle can be improved.