The change of water condition directly influences the composition and succession of regional vegetation communities. In this study, the Xiliaohe Plain was selected to systematically analyze the succession of vegetation's ecological pattern under the change of water condition in semi-arid area. Based on zonality theory and runoff formation principle and combined with field investigation of vegetation, the main community composition of zonality, non zonality and transitional vegetation in Xiliaohe Plain was analyzed in this study. It was concluded that: under the condition of sufficient recharge from rainfall and groundwater, the vegetation communities mainly include meadow vegetation communities and shrub & subshrub communities; when the groundwater depth is decreased to the level which is unable to recharge water for vegetation, there will be succession of the original zonal community; when there is abundant recharge from rainfall and underground water, the vegetation communities mainly include the hankow willow, artemisia halodendron, etc; when the succession was finished and became stable, the zonal vegetation represented by Leymus chinensis community and stipa grandis community was formed.