Abstract: Phragmites australis is a common species in the Songnen Plain of China. Two research habitats were chosen in this arid area. One was a single dominant species community in which, there was some seasonal stagnant water, the other was a Leymus chinensis + P. australis community, growing in alkaline soil with little or no stagnant water. Large random samples taken at the end of the milk stages were quantitatively analyzed for characteristics of reproductive ramets of P. australis from these two different arid habitats. There were significant differences in ramet height, module biomass, total ramet biomass, ratio of reproductive growth and allocation of module biomass in the two habitats, but not flower length or flower biomass. In the both habitats, the variation coefficient of flower biomass was the largest in absolute quantitative characters (57.73%) in the P. australis community and in the mixed community (49.87%) while the variation coefficient of reproductive allocation was the largest in terms of relative quantitative characters (36.17% and 39.44% respectively). There was a positive correlation between flower length and ramet height, but negative correlation between ratio of reproductive growth and rarmet height. Module biomass allocation, reproductive allocation and productive allocation, productive allocation and stem biomass allocation all showed significant allometry, which could be described by a power function (Y=βX^α) regardless of habitat. P. australis populations had the best ability to regulate reproductive allocation in different habitats, reflecting the strategies of the plants growth and reproduction.