Abstract: The temporal and spatial distribution of chlorophyll a (Chl a), phytoplankton community and environmental factors in the Yellow River Estuary were investigated on four ecological surveys, with the purpose of understanding the effect of Water and Sediment Regulation Scheme (WSRS) on phytoplankton community and abundance. Four surveys were conducted on the 16^th of June, 7^th and 20^th of July in 2015 (WSRS year) and on the 14^th of July in 2016 (normal year without WSRS). The concentration of Chl a showed an increasing trend from before to during phase of WSRS, followed by a decline at the after phase. The spatial distribution of Chl a displayed a decreasing trend from inshore to offshore before WSRS to uniform distribution after WSRS. The concentration of Chl a in 2016 was much lower compared with similar period of 2015, and the high value area distributed in the southern inshore area. The identified species of phytoplankton increased along with the progress of WSRS, and an obvious succession of phytoplankton community were observed in the study area. Navicular spp. was the dominant species in all four survey, and other dominant species were Synedra spp., Chaetoceros sp., Coscinodiscus subtilis, Chaetoceros affinis, Asterionella japonica and Chaetoceros curvisetus respectively. Temperature and dissolved inorganic phosphorus (DIP) were the most important environmental factors affecting phytoplankton community and abundance before WSRS, while the influence of dissolved inorganic nitrogen (DIN), DIP and DIN /DIP increased during WSRS, and the dissolved inorganic silicon (DSi), DSi/DIN and temperature became the key environmental factors after WSRS.