Abstract: Large marine structures such as offshore floating wind farms in deep sea areas have effects on navigation safety of ships.Among which sheltering effects induced by the wind farms have drawn attention of maritime administra-tion.Considering maritime environment and distribution of wind turbines,characteristics of maritime radar wave attenua-tion in offshore wind farms have been studied through theoretical analysis and numerical modeling.A comparison between model simulations and field measurements at Shanghai Donghai wind farm verified validity of this method.Site selection of the offshore wind farm is further discussed and a case study of Shanghai is presented.Comparing the influences of off-shore wind farms on ship navigation safety,an optimal layout plan is confirmed and adopted by the major demonstration project of offshore wind power in Shanghai.