The solubilities of the K2Cr2O7 + CrO3 + KNO3 + HNO3 + H2O system at 0 degreesC, 25 degreesC, and 45 degreesC were determined, and the phase diagrams were constructed. Furthermore, analyses and discussions are made on the crystalline areas in the phase diagrams. Based on the solubility data, the technique of a new cleaner process for manufacturing chromium trioxide and potassium nitrate simultaneously by decomposing potassium dichromate with nitric acid was evaluated.