In order to improve the efficiency of determination of insoluble impurities content, and to save washing time of oil splotch on the surface of filter paper, Soxtec Soxlet leaching apparatus was researched to substitute the method of washing splotch on the filter paper surface prescribed in GB/T 15688-2008, and the results obtained with the two different methods were compared. The result showed that the result from Soxtec leaching test was precise and had good reproducibility, and at least 5 h shorter with continuous treatment of 6 samples, less reagents amount and pollution. For dark grease without decoloration, the pigment on filter paper can be washed off completely by Soxtec leaching. Therefore, Soxtec Soxhlet leaching apparatus will achieve the higher efficiency when analyzing the content of insoluble impurities in several oil samples.