The sample to be tested is converted to pentavalent arsenic ions in different forms and valence states of arsenic in the sample to be tested after high temperature and high pressure digestion reaction in the presence of oxidizing agent. Under acidic conditions, the arsenic ion reacts with the color developer to produce a light yellow complex. The complex has maximum absorption at a specific wavelength, and the total arsenic content in the sample is calculated by photoelectric colorimetry according to Lambert-Beer law.