The invention discloses an external rotor motor cooling device, and the device comprises a stator shaft with two water guide holes; an inner water sleeve which is located outside the stator shaft, and is provided with a water incoming channel and a water outgoing channel, wherein the water incoming channel and the water outgoing channel are respectively communicated with the two water guide holes, the periphery of the inner water sleeve is provided with a clip-shaped water channel communicated with the water incoming channel and the water outgoing channel, and the inner water sleeve is in interference fit with the stator shaft; and an outer water sleeve. The clip-shaped structure of the water channel enables the heat dissipation of the motor to be more uniform, and avoids the axial temperature gradient, thereby improving the heat dissipation efficiency. In addition, the water incoming channel and the water outgoing channel are disposed at the central part of the inner water sleeve, thereby effectively reducing the axial size of a supporting part of the inner water sleeve, optimizing the structure of the motor, and facilitating the layout of the water channel. The stator shaft is in interference fit with the inner water sleeve, thereby guaranteeing the stability of the connection of the water incoming channel and the water outgoing channel, improving the sealing performance between the water incoming channel and the water outgoing channel, reducing the weight of the motor, and reducing the production cost.