A large dinoflagellate bloom were found in Fujian Province in January and February of 2009. Water temperature,pH,dissolved oxygen,permanganate index, ammonia nitrogen,total nitrogen,total phosphorus and algal cell density,(hlo-rophyll-a and other factors were nnmitored. Dominant species, Peridirxiopsis penardii, cell density reached 0. 1 x 10⁵-333 x 10⁵cells/L,and total nitrogen concentration was 2. 50—8.65 mg/L,total phosphorus wncentration 0.09-1. 15mg/L.In addition, pH,dissolved oxygen unconventionally increased in more than a month duration, By correlation analysis, cell density of P. penardii and temperature(r=-0.323,P=0.027), pH value (r=0.327,P=0.025)and total nitrogen(r=0.316,P=0.030) were significantly correlated. Partial correlation analysis showed that cell density of P. penardii amt water ternperature was significantly negative corrrlation(r=-0.4894, P=0.008).The results showed that the increase of pH and dissolved oxygen was the phenomenon of dinoflagellate bloom, and total nitrogen may be the growth limiting factors of dinoflagellate, and changes in air temperature amt water temperature was the important reason of occurence of dinoflagellate bloom. Other factors, drought of the in-vestigaliun area, slow watrr flow dense, coupled with sufficient nutrients and suitable temperature, led to occurrence of dinoflagel-late bloom.