The Pearl River Estuary is one of the world’s most complex estuaries and the overall flow simulation is more difficult.This paper describes the development of the Pearl River River estuary,the overall trend of a 2-D coupled mathematical model,and large overall tidal model.The two technologies complement each other and better solves the whole estuarine tidal motion simulation problems.Taking the untra-large river-crossing engineering,the Hong Kong-Zhuhai-Macao Bridge for example,this paper introduces the application of the two models.Introducing the aperture coefficient to control the engineering of complex boundary flow in the mathematical model,we achieve a good simulation effect.