Crystallization is one of the primary processes for producing p-xylene. For the existing p-xylene crystallization kinetics，parameters were all acquired by regressing the profile data of temperature and concentration changes in the crystallization process with non-linear optimization method. Due to the lack of p-xylene crystal particle size distribution information，the accuracy of these crystallization kinetics parameters can hardly be guaranteed. In this paper，the p-xylene crystal size distribution data in the crystallization process are collected with an OPUS on-line particle size measure instrument based on ultrasonic spectroscopy analysis principle. The p-xylene crystallization kinetics is investigated by the method of moments through seeded batch cooling crystallization experiments with a binary mixture of p-xylene and m-xylene，in which the original p-xylene concentration is 82%(mass). The kinetic equations of p-xylene are obtained by regressing the experimental data with the multiple linear least square method. The results suggest that in the melt suspension crystallization process of p-xylene，the relative supersaturation has a larger effect on the crystal nucleation rate than the crystal growth rate. The agitation rate also has prominent effect on the nucleation rate，while the magma density does not.