Abstract: From July 23rd to July 29th, 2019, a Chattonella marina-dominated algae bloom was detected in the Qinhuangdao coastal area. We investigated the relationship between C. marina abundance and environmental parameters such as rainfall, water temperature, salinity, turbidity, pH, dissolved oxygen (DO), chlorophyll a, and dissolved inorganic nutrients in this study. The data revealed that rainfall on July 23rd was the most important component for the bloom's formation. Inflows changed the concentration and structure of nutrients significantly after the rain. Inflows enhanced the concentrations of NO₃-N, NO₂-N, dissolved phosphate, and the ratio of NO₃-N to total dissolved nitrogen in the seawater, allowing C. marina to proliferate. Furthermore, Spearman rank correlation analysis revealed that the abundance of C. marina was positively correlated with DO (r = 0.85) and pH (r = 0.77), significantly (0.01<p<0.05). The results indicated that using environmental elements sensed by buoys to monitor algal blooms is a viable option. The dominating species of phytoplankton communities during the bloom changed from Leptocylindrus danicus and Chaetoceros didymus to Leptocylindrus danicus and C. marina, and subsequently to C. marina. We hypothesized that the distinct reproductive and nutrient assimilation strategies between C. marina and diatoms facilitated the bloom of C. marina.