Abstract: As one of the four most famous historical hydrological engineering projects,theTuoshan Weir,sitting at Ningjiang Town,Ningbo City,is well preserved with normal operation up to now.From its construction at 833 AD,Tang Dynasty,it plays roles in isolation of salty(sea)water,prevention of flooding and irrigation in this area.From viewpoints of scientific plan,design and construction,this paper presents the high level of wisdom recorded in this hydrological engineering from 8aspects as hydraulics,mechanics,etc.