The rich natural resources that occur in the East China Sea (ECS) provide great economic benefits to the associated coastal districts; therefore, research on the water quality in this region is of great significance. As biological indicators of water quality, information regarding temporal and spatial distributions of phytoplankton biomass and growth cycles, as well as modifications caused by climate change is important for understanding the ecology of the ECS. Many researchers have been concerned about the characteristics of phytoplankton blooms in the North Atlantic Ocean; however, there are few relevant studies in this region. The present study occurred during a period of phytoplankton bloom in the ECS and provides a significant reference value for an ecologically representative area. The present study selected nine regions with the same area at different geographical locations, latitudes, and ecological characteristics, and applied chlorophyll a (Chl-a) data from Sea-Viewing Wide Field-of-View Sensor and Moderate-Resolution Imaging Spectroradiometer to analyze the spatial-temporal variation of phytoplankton biomass and phytoplankton bloom phenomenon in the ECS during 1997-2015. The Gauss curve model was adopted by fitting the data collected to obtain the time of bloom initiation, bloom peak, bloom completion, and bloom duration in the ECS. The Gauss curve fitting model was applicable to conform to the Gaussian distribution of the data. To test whether the dataset accorded with a normal distribution (Gaussian distribution), the study applied the Kolmogorov-Smirnov test. The single-peak moving Gaussian model was applied to fit the spring and summer algal bloom outbreaks and define the phytoplankton blooms at the beginning and end of the marker for Chl-a concentration to reach a peak of 20%. The research demonstrated the distribution pattern at the spatial scale, with phytoplankton biomass in the open sea being lower than that in the offshore area. The areas with maximum biomass were the seas of the Yangtze River estuary, the Taizhou region, and the two areas closest to the Yellow Sea. The areas with minimum biomass were the seas of the Nanji Islands and Taiwan Strait. Therefore, the closer the phytoplankton was to the South China Sea, the lower was the biomass. Algal blooms occurred in the Yangtze River estuary from June to September and in the Yangtze River estuary in May and from July to August. Phytoplankton blooms at Taizhou Island occurred during May and July. The algae in the eastern part of the ECS occurred from November and December to January and February in the following year. Phytoplankton blooms at Nanji Islands concentrated during February and March, and the ECS algae in the northern areas between May and June. The biomass of phytoplankton in the northern outer seas was low and algae were mostly present in March and April. In general, the two sections of the research region, which were divided by the Nanji Islands, demonstrated the same regularity, the time taken for phytoplankton to reach peak biomass was prolonged, and the duration of the phytoplankton blooms increased from high latitudes to low latitudes.