Abstract: Crystal size distribution (CSD) transients and internal instability of continuous crystallization processes were studied systematically. The dynamic models describing continuous crystallization were solved by using some new mathematical techniques. And a software was developed which can simulate the sustained limit-cycle behavior of crystallization and the transients in CSD caused by outside disturbances. By means of this software, the influence of various system parameters on CSD stability and the causes of cycling were studied. Simultaneously, transient responses of CSD for a step change in outside operating condition, such as feed flow rate and concentration, product removal rate, fines destruction rate, classifier flow rate, etc., were investigated in detail. The results observed experimentally in a 200L KCl complex crystallizer and a 10L NH4Cl complex crystallizer in this study and the experimental data presented by previous researchers verified that our softwares are suceessful.