The edge effects of plant communities were investigated in a wetland-dry grassland ecosystem of Siertan wetland in Yanchi County，Ningxia Hui Autonomous Region． Based on the importance values，the indices of abundance，diversity and ecological dominance were calculated to analyze the changes and the major environmental factors of plant community structure among three strips and three lines in the ecosystem． The calculated indices show that the vegetations of the investigated area were growing well during the years from 2005 to 2007． However，the exuberant growth had been retarded from 2008 to 2010． Among these five years，the vegetation in 2007 exhibited the best growing condition，while that in 2010 showed the worst． The edge effect was amplified apparently in the community ecotone of wetland and arid grassland，where had the highest ecological dominance (SP)，richness indices (R) and diversity (SW) indices． The dry zone was the most disturbed area by the railway construction． Observations indicated that the changes of vegetation growth in the ecotone were highly related to the amount and frequency of the precipitation．