High-quality utilization method for waste oil

The invention provides a method for preparing oil-based polyol ester by virtue of gutter oil and using the oil-based polyol ester as basic lubricating oil so as to add treatment and utilization channels for gutter oil and realize the high-quality utilization of gutter oil. The method for preparing the oil-based polyol ester by two-step transesterification reaction comprises the following steps: sequentially adding biomass-based raw materials, methanol and a catalyst into a reaction flask, and performing transesterification reaction to obtain biomass-based methyl ester; sequentially adding the biomass-based methyl ester, polyol and a catalyst into the reaction flask, and performing transesterification reaction to obtain biomass-based polyol ester. The biomass-based raw material comprise gutter oil, acid cottonseed oil and vegetable oil foots/soap, and can be utilized in a high-quality manner, and the prepared biomass-based polyol ester can be used as a raw material of biomass-based lubricating oil.