Abstract: At the end of run of the hydrogenation unit of lubricating oil, due to the fact that the hydrocracking tail oil cannot be blended, the nitrogen content in the feed of isomerization was excessive, resulting in unqualified pour point of the base oil and hot spots in the catalyst bed of the hydrocracking reactor. The measures of increasing the temperature of hydrocracking and isodewaxing reactors and using the low nitrogen second-line oil of vacuum distillation tower were proposed. Those methods make the nitrogen content in isomerization unit feed less than 2μg/g, the pour point of base oil not higher than -15 °C，and there are no hot spots in cracking catalyst bed.

Key words: lube oil hydrogenation, nitrogen content, base oil pour point, end of run, hydrocracking tai oil