Start up behavior of NaCl-Ethanol-Water salting out system in a CMSMPR（Continuous Mixed Suspension Mixed Product Removal） crystallizer was investigated using kinetic equations and the population balance equation. While the kinetic equations can be defined experimentally from steady state crystal size distribution, lack of sensitivity in previously analyzed steady state data resulted in two problems for fitting start up data :(1) absence of homogeneous nucleation effect which should be important in start up. (2) absence of size dependence effect of growth Tunction for very small particle sizes. By simultaneously fitting start up data and steady state data, more realistic kinetic equations were obtained.