Abstract: Based on the marine monitoring buoy data of the red tide process of Karlodinium digitatum in Putian sea area in 2022 and the manual monitoring data,potential reasons of outbreak of red tide were discussed.Before the red tide,the water temperature and salinity in Putian sea area were lower than that in the same period of previous years.With the rapid rise of water temperature and salinity,K.digitatum rapidly proliferated and accumulated to form a red tide under the favorable conditions of weak light conditions,relatively stable hydrological conditions,abundant nutrients(especially ammonia nitrogen)brought by precipitation,and aggregation caused by meteorology and tide.It was suggested that this K.digitatum red tide in Putian sea area might have been triggered by a synchronous appearance of optimal climatic,nutritional and hydrographic conditions.The concentration of chlorophyll-a reached 63.90 μg/L,while DO and pH significantly increased during the red tide,with the maximum value reaching 10.83 mg/L and 8.34,respectively.During the extinction period of red tide,with the continuous decrease of water temperature,wide fluctuation of salinity,the breaking of relatively stable hydrological conditions and the low nitrogen phosphorus ratio in the sea area,the red tide of K.digitatum rapidly disappeared.The K.digitatum red tide originated from Gangnan sea area,and spread to other sea areas with tide and current.Huge mortality of fish has been caused by K.digitatum in Putian sea area,when the cell density was higher than 10⁵ cell/L.