Sodium dichromate dihydrate,one of the most important chromate compounds,can be widely used in wood preservation,leather tanning,metal finishing,and refractory.1-3 As a raw material,sodium dichromate dihydrate can also be used for the manufacture of both hexavalent and trivalent chromium products.4-5 The quality of these downstream products depends largely on the purity of sodium dichromate dihydrate.The high quality sodium dichromate dihydrate can be produced from industrial crystallization by operating crystallization conditions within the metastable zone throughout the crystallization process.6-8 Therefore,the investigation of Metastable Zone Width (MSZW) in terms of the separation and purification of sodium dichromate dihydrate is of theoretical and technological importance.