Abstract: The total sulfur content in petroleum products by energy dispersive X-ray fluorescence spectrometry was determined. The sample can be determined by low or high sulfur content, and the uncertainty of total sulfur that be introduced in petroleum product was evaluated. The uncertainties are quantified by relative standard uncertainties, and the extended uncertainty of the standard is obtained by calculation, which can provide reliable guarantee and reference for the report of final data. The analysis result shows that the uncertainty of this method is mainly caused by the fitting curve, the counting rate, the repeated determination of samples, the error of total sulfur content of the standard samples, and the repeatability of the instrument. Under the condition that the confidence probability is 95% and the inclusion factor k=2, for the samples with total sulfur mass fraction less than 1000 mg/kg, and the result is (816±9) mg/kg, and for the samples with the mass fraction between 0.1% and 5.0%, the result is (2.640±0.045)%, both of the extended uncertainty corresponding to both are lower than the requirement of repeatability of the standard, indicating that the data produced by the instrument has good reliability.