The samples to be tested are oxidized to cadmium ions in different forms and valence states in the samples to be tested under neutral conditions and in the presence of oxidizing agents, after high temperature and pressure reactions. In a strong alkaline solution, cadmium ions react with the color developer to produce a yellow-green complex. The complex has maximum absorption at a specific wavelength, and the total cadmium content in the sample to be tested is calculated by photoelectric colorimetry.