The frequent occurrence of harmful algal blooms (HABs) in China’s coastal areas has caused major losses to the economy and society and has seriously threatened the coastal marine environment. Based on 30 years of relevant statistical data and satellite remote sensing data from 1990 to 2019, we analyze spatial–temporal distribution of HABs in China’s coastal areas. Our results show that 1557 HABs occurred in China’s coastal areas from 1990 to 2019: (1) 961 HABs occurred in offshore China from 2001 to 2012, a period with many HABs, accounting for 62.00% of the HABs of the study period. The numbers of HABs (1998 to 2019) in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea were 198, 133, 813, and 249, respectively. 536 HABs occurred from April to September, accounting for 88.00% of the total occurred from 2009 to 2019. (2) Spatially, based on the kernel density estimation, HABs were mainly concentrated in Bohai Bay, the Yangtze and Pearl River deltas, and other regions with relatively dense populations and relatively developed economies, especially in Zhejiang Province and in the Yangtze River Estuary. Imagery-derived information on the build-up of HABs provides coastal communities with objective information to plan and deal with the adverse environmental and health effects associated with an HAB.