Today, the development of design and operation of industrial crystallization processes requires data on the kinetics of crystal growth and understanding the effect of operating conditions on kinetics and rate of crystal growth. In this paper, it is aimed to investigate the factors influencing on the mechanism of growth rate of potassium sulfate in the fluidized bed crystallizer. Several important parameters including the height bed, solution PH value and presence of impurity is considered. In fact, the quality (size, shape and purity) of the product is affected by many parameters influencing the growth mechanism such as hydrodynamic conditions, pH of the crystallizing solution, and the presence of additives and impurities. The results show that larger bed heights generate higher growth rates. Also, the variation of the PH value of the solution changes the growth rate significantly. In addition, one can conclude that the presence of small amounts of impurity material such as chromic ions can decrease the growth rate considerably.