The Huang-Huai-Hai plain is one of the largest alluvial plains and it is also an important agricultural region in China.It is mainly Formed by the flooding and sedimentation of water system of the Huang,Huai and Hai rivers.Due to the flat relief and poor drainage,there is a large area of saline soil of which the groundwater is salty in the central and eastern portion of the plain.This area belongs to the semihumid and semi-arid climatic zone.Owing to the influence of Pacific monsoon,it is dry in spring and rainy and flooding in summer and autumn.The crop yield is quite unstable.Under the specific biogeographical condition,an unique regional ecosystem is formed in the plain;and the alternation of drought,flooding,salinization and alkalination induce the extreme complication and unstability of the ecosystem in this region which seriously influences the development of agricultural production and national economy.