Abstract: The effects of the reaction molar ratio of ammonium sulfate and the content of sodium chloride on the purity and yield of potassium sulfate were investigated in this article. The growth rate of single crystal potassium sulfate was in-situ observed with a stereo microscope in a flow system to find desirable conditions for the rapid growth of potassium sulfate crystals. The results indicate that the recovery of potassium sulfate is about 80% when the molar ratio of 2KCl to (NH₄)₂SO₄ is 1:1. Na Cl has significant influence on the purity and recovery of potassium sulfate,and reduces the quality of the product. To accelerate the growth of potassium sulfate crystals,the saturation of potassium sulfate and the solution flow rate should be increased.