In this work, the effect of temperature on the crystal growth rate of potassium sulfate in aqueous K 2 SO 4 and KCl-K 2 SO 4 solutions is analyzed. The crystal growth rate equation of K 2 SO 4 is developed on the basis of the difference of chemical potentials of K 2 SO 4 at the solid-liquid interface. The Lu-Maurer model is used to predict the activity coefficient of K 2 SO 4 . The crystal growth rate of K 2 SO 4 in aqueous K 2 SO 4 solution decreases, then increases with increasing temperature, and reaches its lowest value around 303.15 K, which is in accordance with previous experimental results. Meanwhile, the optimal crystallization temperature of K 2 SO 4 in aqueous KCl-K 2 SO 4 solution is discussed. An effective method is found to increase the yield of K 2 SO 4 by increasing the crystallization temperature to 333.15 K.