What is marine plunger couple? Marine plunger couple includes plunger and sleeve. The sleeve forms an axial mid-hole. The plunger is movably inserted into the axial mid-hole, which can rotate and slide up and down relatively. There are oil inlet holes on the sleeve. The upper part of the axial mid-hole is connected with an oil outlet. There is a sealing ring in the axial mid-hole, and the sealing ring is attached to the oil inlet hole. The outer surface of the sleeve is matched with at least one first sealing ring for ensuring the sealing of the low pressure oil chamber, and the lower part of the sleeve is matched with the plunger by an oil scraper. The invention adds a ring groove on the plunger to increase the lubrication performance of the plunger and sleeve; the sleeve is sealed by an axial middle hole, which improves the processing performance and improves the processing efficiency under the requirement of high pressure sealing; the invention has the advantages of novel structure, good performance, good sealing effect, small volume, accurate oil supply, simple structure, easy manufacture and stable injection.