Abstract: The crystallization kinetics of hexammoniate magnesium chloride (MgCl2·6NH3) was investigated in a MSMPR crystallizer. The birth and death functions of agglomeration and breakage were used in the population balance model of the process. By changing the expression of current breakage birth and death function, we proposed an improved binary random birth and death function model of agglomeration and breakage, without the traditional equal-volume-breakage assumption. The parameters of crystallization kinetics of MgCl2·6NH3 were obtained by solving the model equations and fitting the particle size distribution (PSD) data.