Abstract: By means of GC-AED, the sulfur-containing compounds presented in the hydrotreated diesels obtained from bench-scale reactor were analyzed, and several questionable peaks were found in the chromatograms. The same questionable peaks were also found in the chromatograms of diesels before and after oxidation and extraction. By the analysis and conjecture it is thought to be the elemental sulfur's peak. Through the analysis of the sample by adding elemental sulfur into sulfur-free oils and washing the object diesels with mercury, these questionable peaks were identified as elemental sulfur. The reason for elemental sulfur formation in the hydrotreated diesels and the effect of elemental sulfur on the analysis of sulfur content of hydrotreated diesels are discussed in this paper. Moreover, if the diesels containing elemental sulfur and/or H2S were selected as samples in non-hydrodesulfurization test, such as oxidative desulfurization test, a wrong conclusion might be made due to the difficulties of removing elemental sulfur by oxidation /extraction. So the diesels not containing elemental sulfur and/or H2S should be chosen as the samples in non-hydrodesulfurization test.