Typically, the industrial evaporation process is operated at a high evaporation rate in a nonequilibrium stable or dynamic state within a temperature range of 323 to 393 K. During this process, both the solubility and the crystallization of salt are affected by organic impurities in the system. In this work, glutaraldehyde, one of the main organic compounds in wastewater produced from the coal chemical, was selected as a representative organic impurity, and the chemical oxygen demand (COD) of glutaraldehyde solution was used to simulate the COD of highly saline coal chemical wastewater. The stable and metastable solid liquid equilibria of the (Na2SO4-NaCl-H2O) system containing the organic impurity at 333.15 K were studied. The results showed that the solubility and supersolubility of Na2SO4 increased with the increase of COD. However, the solubility and supersolubility of NaCl had begun to increase when the COD value is around 450 mg L-1. When the COD value reached to 3290 mg L-1 (the content of actual wastewater), the solubility and supersolubility of both Na2SO4 and NaCl exhibited a dramatic change. Meanwhile, the metastable zone widened and the salt-forming zone moved remarkably. These results suggest that when the removal of organic impurities in the system cannot be achieved cost-effectively, the effect of organic impurities on NaCl salts in the system can be significantly decreased by reducing the COD value to within 450 mg L-1 before salt crystallization.