Most oar-hunging fishing boats are geared by agricultural oar-hungs. Oil pollution caused by the leakage of the upper gear-case of the oar-hung and the diesel engine is limited, and the main cause is the leakage of lubricating oil into the water when the tail-shaft rubber seals are damaged due to foreign matter entwined with the oars. In order to control the oil leakage of oar-hungs on fishing boats, based on the comprehensive analysis of oil leakage causes of oar-hungs and the thereby proposed improvement measures, the air permeability of the upper gear-case and the tail-shaft seals protection of the lower gear-case of the agricultural oar-hungs were improved. The air permeability cap for the small loader was used to optimize the previous improvement of adding suction apparatus to the cover plate of the upper gear-case of oar-hungs, which not only solved the problems of lubber oil expansion during operation, but also tackled the problems of leakage during handling and high cost during purchasing. The setting method of non-contact labyrinth sealing device at the tail-shaft rubber seals and end cover of the lower gear-case of the oar-hung was elaborated, the labyrinth seal can not only protect the shaft contact type rubber seals from accidental damage, but also reduce oil leakage speed when the rubber seals are damaged. The experimental results show that the improved schemes of the air permeability cap on the upper gear-case, the labyrinth seal on the lower gear-case and other improvement measures effectively solved the problems of oar-hung oil leakage. This study used relatively small costs in oar-hung transformation but solved the big oil pollution problem of oar-hungs, and could be further popularized.