Spartina Alterniflora salt marsh of Jiangsu coast,the biggest area in China,covers an area over 1.25×104ha.Spartina Alterniflora usually spreads between the mean spring high tidal level and the mean tidal level.Jiangsu coast has a long history of reclamation.Nowadays,much of the supra tidal flats have been reclaimed,and native salt marsh decreased gradually.Spartina Alterniflora has become the main vegetable species of salt marsh in Jiangsu coast.Meanwhile,seawalls of the newly reclaimed areas were built on the gradual lowering tidal flat,hence the construction of the seawalls of reclamation becomes more and more difficult.Spartina Alterniflora has a strong vitality and productivity,with an expanding dominance on tidal flat environment.Its standing condition,and ecological niche are the indicators of dynamic condition of the tidal flat,height of the outer line of the area to be reclaimed as well as the direction of seawall of the reclaimed area.Taking Haizhou Bay Top as a case in this paper,three fieldwork sections and eight phases of satellite imageries from 1978 to 2003 are collected to analyse the dynamic change of coast and spread of Spartina alterniflora along Haizhou Bay.The result indicates that the primary condition of the tide flat for inning becomes possible because of the steady elevation of the coast.The rate of elevation is 20m/a,the area of high intertidal flat outside the old seawall is 300ha,the width of Spartina alterniflora Loisel distributed belt outside intertidal flat is from₂00m to 1 200m.The height of the outer line of the proposed reclaimed area is 2.84m according to the mean high tide level and ecological niche of Spartina alterniflora.However,the complexity of open,type bay,including the influence on Linhong River estuary and other drainage sluice as well as salt marsh restoration should be taken into account in tideland reclamation along the Haizhou Bay Top.