According to a larger analysis error by colorimetric method in determining arsenic in sulfur in SINOPEC Jinan Company, the new technology microwave digestion and hermetic microwave digestion was used to process samples. It was introduced that processing conditions of microwave digestion for treatment of industrial sulfur and operating conditions, influence factors and advertent questions of atomic fluorescence spectrometric method for determination of trace arsenic in sulfur. The limited detection of microwave digestion for processing samples is 0.01μg/L; RSD is 2.4%. This method to detecting arsenic in sulphur has the advantages of high sensitivity, high accuracy and wider linearity.