Abstract: Water quality condition is of great significance for protection of marine ecological environment and sustainable development. In this study, from the perspective of water transparency (Z_sd), we proposed a new method for evaluating water conditions based on long time series MODIS optical satellite remote sensing data in the Eastern China Seas. The method classifies water quality using transparency and trends, and the water can be divided into High and Increasing (HI) type, High and No change trend (HN) type, High and Decreasing (HD) type, Low and Increasing (LI) type, Low and No change trend (LN) and Low and Decreasing (LD) type, were used to analyze the water quality in the Eastern China Seas and its influencing factors. The results showed that most of the coastal waters of the Eastern China Seas are LN type, while the waters in Jiangsu Coast (near Lianyungang) are LD type in the past 20 years. The offshore waters mostly beyond to HN type, while some areas of the South of South Yellow Sea and the East China Sea shelf generally showed HD type waters. Phytoplankton and suspended sediment are the dominant influence factors of the water condition in the offshore and coastal waters, respectively; and in the Zhejiang-Fujian coast, the water condition is probably modulated by the both of phytoplankton and suspended sediment.