The invention relates to a detection method of vehicle petrol cleanness, which comprises heating and evaporating test oil sample at poor oxygen state until being evaporated completely, weighting residues weight, using organic solvent to extract the residues after the evaporation until no residues dissolves in the organic solvent continuously, weighting the residues weight, and evaluating the cleanness of the tested oil sample. The inventive method can effectively and accurately test petrol cleanness, which is simple, quick and economic, with wide application.