The evaporation crystallization of K2CrO4 from KOH aqueous solution is one of the key units of the chromate cleaner production process developed by the Chinese Academy of Sciences. The vapor pressure of the KOH + K2CrO4 + H2O system was determined so as to optimize the evaporation operation. On the basis of the experimental results, the relationship between the vapor pressure and the temperature as well as the concentrations of KOH and K2CrO4 were determined as log(P/kPa) = 7.52- 3.62 x 10(-2)(C-KOH/mol . L-1) - 7.83 x 10(-2)(C-K2CrO4/ mol . L-1) - 2055.74 K/T wherein C-KOH ranges from (0.8 to 10) mol . L-1, C-K2CrO4 ranges from (0 to 2) mol . L-1, and T ranges from (328.15 to 368.15) K.