Aimed at the problem of excessive demulsification degree in daily inspection of lubricating oil of the hydraulic generator governor in the storage power station,the relevant indicators of oil were tested.Based on the correlation analysis of the varnish tendency index,it is concluded that the reason for the excessive oil demulsification is caused by the oxidation deterioration of oil.An electrostatic oil filter was used to filter the used oil of governor with excessive demulsification degree.It is found that the demulsification index of the used oil after filtration meets the standard requirements,and the film tendency index is also in the normal range,which further verifies that the unqualified demulsification index of the oil is caused by its oxidation products.