The common valence states of chromium compounds are trivalent and hexavalent. In water, hexavalent chromium is generally in the form of cr2o72-, cro42- and can be transformed into each other by the influence of pH value, temperature, redox substance and organic matter. Chromium is one of the necessary trace elements in organism. The toxicity of chromium is related to its valence state. Hexavalent chromium has strong toxicity, which is a carcinogen and is easily absorbed by human body and accumulated in vivo. It is generally believed that hexavalent chromium is 100 times more toxic than trivalent chromium. However, for fish, trivalent chromium compounds are more toxic than hexavalent chromium. When the concentration of hexavalent chromium in water reaches lmg/l, the water is yellow and astringent; When the concentration of trivalent chromium reaches lmg/l, the turbidity of water increases obviously. The natural water on land generally contains no chromium; The average concentration of chromium in seawater is 0.05 μ G / L, lower drinking water. The industrial pollution sources of chromium mainly come from the waste water of chromium ore processing, metal surface treatment, leather tanning, printing and dyeing, photographic materials and other industries. Chromium is an important index of water pollution control. The determination methods of chromium in water mainly include diphenylcarbazide spectrophotometry (gb/t 7467-87), atomic absorption spectrophotometer, ammonium ferrous sulfate titration, etc. Spectrophotometry is a standard method at home and abroad; Titration method is suitable for water samples with higher chromium content.