Abstract: Based on the final analysis data(FNL) from National Centers for Environment Prediction (NCEP) reanalysis data and the improved NPS diagnostic model, the seasonal and monthly changes of evaporation duct over East China Sea are analyzed. The distribution of ducts is discussed to provide reference for radar detections and radio communications. The results show that the evaporation duct height of northwest is higher than southeast in spring and summer. Spring is the season with the highest duct height. The maximum of evaporation duct height over the northwest of East China Sea is in May, which is 20 m. For the central East China Sea, the lowest evaporation duct height is in June. On the contrary, higher in southeast in autumn and winter. There are obvious seasonal, monthly and regional differences in the height of the evaporation duct over the East China Sea. This may be related to the geographical characteristics of the East China Sea and climate change.