The invention discloses a groove external electroplating technology of a cylinder body. Groove external electroplating is adopted, the inner surface of the cylinder body is used as a cathode and sleeves an anode, electroplating liquid flows through an annulus clearance between the inner surface of the cylinder body and the outer surface of the anode to form an electroplating environment, electrification is implemented, and then electroplating is finished. According to the scheme, the electroplating environment is formed by the flowing electroplating liquid, by the flowing electroplating liquid, real-time substitution of positive ions on a plating layer is guaranteed, concentration difference between the positive ions on the surface of the plating layer of the cathode is not changed basically, large concentration difference is avoided, the thickness of the plating layer is variable and controllable, meanwhile, by the undifferentiated concentration, compactness of the plating layer is guaranteed, the flowing electroplating liquid can balance change of the PH environment of the plating liquid caused by the hydrogen evolution effect, poor binding force is avoided, and electroplating quality is guaranteed.