Phragmites australis, as a widely distributed species, has a high degree of intraspecific variation in functional traits and is able to respond to external climatic and environmental changes and adjust its adaptation strategies on time. The plant economic spectrum can reflect the adaptation strategies of resource acquisition and storage of plants in different climatic regions, and provide a scientific basis for understanding the ecological differentiation of plants in different habitats and their adaptation mechanisms. In this study, the morphological traits, nutrient contents and stoichiometric ratios of P. australis in lakes and lakeshore wetlands of semi-arid and arid climatic regions from east to west in Inner Mongolia Plateau were investigated to reveal the variability of plant functional traits at different regional scales and the influencing factors, and to reveal the ecological adaptation strategies of P. australis in different regions through plant economic spectrum. The results showed that soil moisture gradient, geographic location and regional scale effected the intraspecific variation of functional traits of P. australis. At the local scale, soil moisture gradients had opposite effects on the response to functional traits of P. australis in the arid and semi-arid regions. At the regional scale, climatic factors dominated the variation of reed functional traits across the latitudinal gradient, while the correlation with soil properties was not significant (P > 0.05). Plant economic spectrum theory is also applicable to the functional traits of various organs and whole plants of P. australis populations at different regional scales, and the acquisition and assimilation of resources is conservative in arid regions, while in semi-arid regions it is an acquisition strategy. This study provides a new understanding of the ecological niche differentiation and drivers of plant populations and ecological adaptation strategies of species at the regional scale, and provides a theoretical basis for the restoration and reconstruction of degraded wetland ecosystems.