The invention discloses a motor-transmission integral transmission system for an electric automobile and relates to a two-gear automatic gearbox planetary gear mechanism. The mechanism comprises two single-row 2K-H planetary gear transmission systems, a front-row gear ring is fixed in a front-row planetary gear transmission system, and motive power is transmitted from a front-row sun gear to a front-row planet carrier for outputting to complete a first-level deceleration. In a back-row planetary gear transmission system, a clutch C1 achieves combination and separation of a back-row sun gear and a back-row planet carrier, a brake B1 achieves fixation and separation of a back-row gear ring and a tank body, finally the motive power is output by the back-row planet carrier, and shifting of two gears can be completed through different combinations of working of the clutch and the brake. The motor-transmission integral transmission system is simple in mode, compact in structure, small in size and light in weight, and meets principles of automobile light weight.