The Sanjiang Plain is the largest area of freshwater wetlands in China,but now it was seriously fragmented because of intensive argricltural activities since the 1950’s.Based on the changed habitat environment,we aim to discern fine-scale patterns of plant species richness on the wetland remnants,and the relationships between species richness,biotic factors and abiotic factors for the purpose of biodiversity conservation and management.A total of 246 1m?1m quadrats was randomly sampled.In a quadrat,abiotic factors including hydrological condition and soil resource variables were measured,meanwhile biotic factors such as plant species richness,community density and important value of the dominant species (IVD) were calculated.Simple regression analysis and path analysis were used to check for the effects and relationship between abiotic factors,biotic factors and species richness.In the quadrats without standing water,species richness was determined by IVD,electrical conductivity,available nitrogen and available phosphorus.IVD is significantly associated with community density and soil water content,while community density is not correlated with any soil resource variables.In the quadrats with standing water,species richness was controlled by IVD and water depth.Furthermore,IVD and community density were significantly influnced by community density and water depth repectively.Different hydrological conditions result in different patterns of species richness and community characteristic.No matter what hydrological condition was,IVD plays a vital role in explaining variance in species richness.Generally,abiotic factors influence biotic factors,and they both determine species richness on wetland remnants.