Abstract: Based on continuous monitoring, this paper analyzed and discussed the process of a Prorocentrum donghaiense bloom, which occurred in Changle Sea Zone of Fujian Province during May 2 and May 10 in 2010. This red tide organism could form red tide under weather condition of intense illumination; this organism mainly utilizes nitrate as its nitrogen nutrient after the formation, and it also has remarkable ability to withstand the stress of low phosphorus in the environment. In addition, the principal components analysis of environmental factors in Changle sea area during the monitoring process showed that limiting factors of this red tide included NO₃-N, NO₂-N, water temperature, salinity, et al.