The invention discloses a double-motor assembly device for an electric vehicle. The device comprises an end cap, a first shell, a second shell, a first motor, a first planetary gear mechanism, a clutch, a second motor, a second planetary gear mechanism, a brake and an output shaft. A vehicle engine is connected with a planetary frame of the first planetary gear mechanism, and the first motor is connected with a sun gear of the first planetary gear mechanism; the second motor is connected with a sun gear of the second planetary gear mechanism, a planetary of the second planetary gear mechanism is connected with the output shaft, the clutch is arranged between the first motor and the second motor, and the brake is fixed to a bottom cover of the first shell; by controlling connection and disconnection of the clutch and the brake, dynamic coupling or decoupling of the engine, an auxiliary motor and a driving motor is achieved, and accordingly various work modes like a pure electric mode, a serial connection mode and a hybrid power driving mode can be achieved; meanwhile, large-transmission-ratio design of the motors is achieved, axial sizes of the motors are reduced, and the cost is reduced.