Preliminary results indicated that chlorophyll-a values were 0.06 - 8.28 mg/m³ (average of 1.33 mg/m³), higher in spring and autumn, lower in summer and winter. Chlorophyll-a contents at the surface are higher than those at bottom. Multiple regression shows that soluble Fe, COD and salinity are the most important factors influencing the variations of chlorophyll-a (followed by DO, t, turbidity) and that Mn, Si(OH)₃-Si,PO₄-P,NO₂-N have significant correlation with chlorophyll-a. In Dapeng Bay, Noctiluca scientillans red tide always occurs in spring. Red tide caused by other organisms, such as Skeletonema costatum, Chattonella marina and Conyaulax polygramma, etc., were sometimes also observed there at that time. The relationships between chlorophyll-a and inorganic andorganic factors and occurrence of red tide are analysed and discussed. The results can be helpful for further ecological research in the bay and for red tide forecasting.