In order to improve the process of producing potassium sulfate with sodium sulfate and potassium chloride by double decomposition method,and increase the purity and yield of potassium sulfate.With industrial grade sodium sulfate（purity≥99.31%） and potassium chloride（purity ≥97.42%） as raw materials,the preparation conditions of glaserite and potassium sulfate were studied.The effects of water addition amount and reaction time on the purity and yield of potassium sulfate and glaserite were investigated.The optimal process conditions for producing potassium sulfate with sodium sulfate and potassium chloride by double decomposition method were obtained as follows：100 g potassium chloride and 106.01 g sodium sulfate reacted at 298 K,the preferred water addition amount was 218.60 g and the reaction time was 2 h.The optimal evaporation amount of sodium chloride obtained by evaporation of metathesis mother liquor was 110% of theoretical evaporation water.The preferred water addition amount of preparing potassium sulfate by glaserite was 322.06 g while the preferred reaction time was 2 h.The mass fraction of K₂O and Cl-in potassium sulfate were 52.74% and 1.31% respectively,which met the technical requirements of premium grade in the standard of Agricultural Potassium Sulfate（GB/T 20406—2017）.