The sample to be tested is oxidized to bivalent copper ion after high temperature and high-pressure reaction in the presence of oxidant in different forms and valence states. Then the bivalent copper is converted to cuprous ions by a reducing agent, and a color developer is added, and the cuprous ions react with the color developer to produce a stable yellow-brown complex. The complex has maximum absorption at a specific wavelength, and the total copper content in the sample to be tested is calculated by photoelectric colorimetry.