The invention provides a mechanical automatic transmission of an electric automobile provided with an overrun clutch, and belongs to the technical field of transmission of electric automobiles. The transmission comprises a transmission control system, a variable transmission mechanism, a gear shift operating mechanism and a reverse gear operating mechanism, wherein the variable transmission mechanism is provided with the overrun clutch and performs two-stage transmission; and the gear shift operating mechanism comprises a centrifugal gear shift operating mechanism and a synchronizer gear shift mechanism, the centrifugal gear shift operating mechanism adopts a mechanical structure, detects a speed of the automobile through gear transmission and produces centrifugal force, and the centrifugal force is combined with spring return force, so that mechanical automatic speed changing is realized. According to the mechanical automatic transmission, performance requirements for a driving motor are reduced, and the efficiency of the driving motor and the dynamic property and economy of the whole automobile are improved; an electric control gear shift mechanism is omitted and replaced with the mechanical gear shift mechanism, so that the production cost is reduced, and the system stability is improved; and simultaneously, the overrun clutch and the synchronizer gear shift mechanism are utilized, so that the power failure time during the gear shift process is shortened, the transmitted torque of the transmission is increased, and the system reliability is improved.