A hydride generation-atomic flourence spectrometry (HG-AFS) method with program temperature graphite digestion/microwave ashing for sample preparation was developed for the determination of total arsenic in alga.Methods The alga, into which 5 ml HNO₃ was added, was heated at 190 ℃ for 30 min with program temperature graphite digestion, then ashed at 550 ℃ for 5 min with microwave using magnesium nitrate as ashing auxiliary agent. The ashes were dissolved with hydrochloric acid and total arsenic was determined by HG-AFS. Results The detection limit was 0.42 μg/L, and the RSD was less than 5%. The recoveries were between 96% and 109%. The arsenic forms were detected in digested alga by program temperature graphite digestion/microwave ashing, the results confirmed that more than 99% of organic arsenic in alga had been digested into inorganic arsenic. The method was applied to determine the total arsenic in two certified reference materials of Laminaria japonica (GBW08517) and laver(GBW10023), and the analysis results were all in the reference range. Conclusion The method had good accuracy and precision, and was suitable for the determination of total arsenic in alga.