The invention discloses an automatic oil coating device of an automobile motor rotor. A transfer device comprises a conveying belt on a tension shaft and a support shaft, a driving device comprises arotation shaft, a driving wheel is fixedly arranged at an end part of the rotation shaft and is provided with convex teeth, the driving wheel is engaged with a first gear, a first convex block is concentrically arranged at an end surface of the driving wheel, the driving device also comprises a swinging piece, the swinging piece comprises a swinging arm and a fan-shaped gear, a brushing device comprises an air cylinder, the air cylinder is arranged below the swinging piece, an oil inlet valve and an oil outlet valve are arranged on a side wall of the air cylinder at one side of an air cylinderpiston rod, an oil groove is formed in the bottom of the air cylinder, the brushing device covers the oil groove, an oil pipe is arranged in the side wall of the air cylinder between the oil outlet valve and the oil groove, an air inlet one-way valve and an air outlet one-way valve are arranged on the side wall of the air cylinder at one side far away from the air cylinder piston rod, and an airspraying head is arranged on a side wall of the brushing device. With the adoption of the automatic oil coating device disclosed by the technical scheme, automatic oil removal and rust prevention areperformed on the motor rotor, and the efficiency is greatly improved.