For the purpose of improving the oil leakage of oar-hung diesel engine and gear box in river, technical upgrading of oar-hung gear box and oil pan was carried out through optimization design, contrast test and other methods. It was mainly to improve the structure of gear box cover plate and the oil pan: install a respirator on the gear box cover plate; choose the appropriate oil-absorbent felt material; add a lining to the oil pan to prevent the leaked residual oil from spreading. Subject to mooring test, navigation and reversing test of 3 oar-hung fishing vessels and contrast test of adsorbed oil-water mixture of oil-absorbent felt of various materials and specifications, the effect of technical improvement after the gear box cover plate was installed with a respirator was obvious. After the improvement, no oil overflow occurred in the air port of the 3 oar-hung fishing vessels. The oil-absorbent felt chosen could quickly adsorb dirty oil but would not adsorb water. The results show that the improvement plan of installing the gear box cover plate with a respirator is feasible and effective and has promotional value; the oil-absorbent felt chosen  is an ideal material to be used together with oil pan and installed on the propeller shaft tube of oar-hung gear box.