Abstract: The oil groove of water pilot bearing of large and medium hydro turbine generator set in operation often has oil leak problem, which causes resources waste, environment pollution, even seriously threatens the safe operation. To ensure normal operation of power generation set of hydropower station, in the consideration on different leak causes, taking the abnormal oil level of water pilot bearing of No.3 hydro turbine generator set of Pubugou Hydropower Station as example, the analysis and research were conducted. In the analysis, through consulting a large number of literature and drawings, field investigation and operation practice, we found out the cause of oil leak. In the light of the oil leak causes, the target treatment technique and measures were developed accordingly and the treatment gained satisfying effects. We introduce the equipment selection, equipment defects, corresponding measures and effects.