The invention discloses a steel pipe external-surface smearing device capable of automatic addition of rust removal oil. The device of the invention comprises a pedestal, a support, a supporting mechanism, a conveying mechanism and a smearing mechanism. The support is fixedly installed on the upper end of the pedestal. Left and right ends of the support are symmetrically connected to a hydraulic telescoping rod A, the inner side of which is connected to the supporting mechanism. The supporting mechanism comprises a cylindrical block, an electric telescoping rod C and a non-skid mat. The smearing mechanism comprises an electric telescoping rod A, a connecting rod, an arc-shaped plate A, an arc-shaped plate B, an arc-shaped chute, an arc-shaped tooth bar, an electric telescoping rod B, a gear, a forward and reverse rotating motor B, an arc-shaped chamber, a chute, a slide block, a smearing roller, a connecting port and a movable block. The upper end of the support is also provided with the conveying mechanism. the device has a novel design, can be used to smear steel pipes with different diameters, has high smearing efficiency and good effect, can effectively prevent wastage of the rust removal oil during the smearing process and also can ensure full smearing of the rust removal oil. Then, the rust removal oil is smeared uniformly, and the device has strong practicality.