In view of the large difference between the oil-water ratio setting and emulsification working condition in the evaluation method of demulsibility property of lubricating oil in the national standard GB/T 7305—2003 and the practical application,considering the practical application factors of demulsibility property of lubricating oil,by changing the oil-water ratio and emulsification working condition,the appearance and interface of oil-water emulsion of four common lubricating oils were observed,the water separation rate and water separation speed,the oil content in water phase and water content in oil phase were determined.Demulsibility of lubricating oil was evaluated by qualitative and quantitative methods jointly.The results show that when the oil-water ratio increases,the water separating speed and water separating rate of the lubricating oil emulsion decrease,the oil content in the water phase and the water content in the oil phase increase,and the change is more obvious when the oil-water ratio is high.Therefore,with the increase of oil-water ratio,the demulsibility of lubricating oil decreases gradually,and the difference of demulsibility between different lubricating oil emulsions becomes larger.Based on the above analysis,a complete evaluation method for the demulsibility property of lubricating oil was proposed.Based on the evaluation method of national standard GB/T 7305—2003,this method increases the quantitative evaluation of water separation rate,water separation speed,oil content in water phase and water content in oil phase under the oil water ratio at the actual working conditions,which can fully reflect the demulsibility of lubricating oil under actual working conditions.