From November 2008 to March 2009, an ecological investigation on the population of Reed Parrotbill (Paradoxornis heudei) was conducted in Chongming Dongtan, Shanghai. And during the study, a correlation analysis between the Reed Parrotbill population and environmental factors was undertaken. One-way ANOVA was used to analyze the impacts of smooth cordgarss (Spartina alterniflora) invasion and reed(Phragmites australis) harvesting on the distribution of Reed Parrotbill population and multi-regression analysis was used to analyze the relationship between the density, distribution of Reed Parrotbill and environmental factors. The results showed that the population density of Reed Parrotbill in Chongming Dongtan was (5.08±3.11)ind/hm2; the reed diameter positively correlated with density of Reed Parrotbill, the reed height and density had significantly positive impacts and food resource hold a positive impact to the distribution of Reed Parrotbill; smooth cordgrass had a negative impact to both density and the bird distribution. The habitat quality of Reed Parrotbill was on the decline due to the smooth cordgarss invasion and reed harvesting. Keeping some patches of reed in good growing condition could facilitate Reed Parrotbill wintering in Chongming Dongtan.