Since the first appearance in 1982, Cochlodinium blooms have plagued the southern coasts of Korea with increasing frequency and duration causing huge damages to the mariculture industry. We simulated the Cochlodinium outbreak in 1998 using an individual-based model. Current fields were provided by a 3D POM circulation model. In situ data were used for boundary conditions and wind. We focused on two processes of blooms: surfacing of germinated cells, and population growth in the advective system. For the first process, vertical movement of the germinated cells was tracked. For the second process, cells were allowed to undergo binary fission according to the growth rate obtained from culture experiments. Nutrient limitation and grazing were also considered. Monte Carlo methods were used for cell division and death. The results show that cells can surface only in the nearshore area regardless of the excystment site. Depending on the surfacing location, blooms can be formed in the different areas. These areas well match the actual HAB-frequent areas. Similar results can be obtained even without nutrient limitation, although the likelihood of bloom increases.