A downhole traction system includes a driving system and a downhole wheeled tractor. The driving system is connected with the downhole wheeled tractor; the downhole wheeled tractor comprises a tractor body, a power unit and a plurality of traction units; the plurality of traction units are arranged along the extension direction of the tractor body; each of the traction units comprises a driving arm, a supporting arm, a supporting wheel, a driving assembly and a supporting assembly; the driving arm and the supporting arm are movably connected with the tractor body; and the supporting wheel is connected with the driving arm and the supporting arm. When the supporting assembly drives the supporting arm to extend along the radial direction of the tractor body under the hydraulic drive action of the hydraulic power unit, the supporting wheel can be abutted against the well wall.