Abstract: Calamagrostis epigejos is a typical clonal rhizomatous plant. It always forms mono-dominant patches in the meadows of the Songnen Plain, China. In this research, a survey of age structures of plant modules was conducted in the late growing season of 2013 and 2014 and analysis was carried out. Age structures of ramets, rhizomes, daughter ramets and buds were classified according to the generation of vegetative propagation. Vegetative propagative ability was calculated by the ratio of the total buds or daughter ramets to total ramets or rhizomes and storage ability of rhizome was calculated by the ratio of rhizome biomass to its length in C. epigejos populations. It was found that ramets in C. epigejos population consisted of two age classes (1st and 2nd age class) and the proportion of number and biomass on 1st age class of ramets was higher than 80%, which was an increasing age structure. Rhizomes could be grouped into three age classes (1st, 2nd and 3rd age class) and the proportion of accumulate length and biomass was the greatest (more than 40%) on 2nd age class, which age structure was stable. Ramet productivity (ramet biomass/ramet number) of 1st age class was 4% higher in 2013 and 21.6% higher in 2014 than 2nd age class, so ramets on 1st age class had greater contribution to the population. Storage ability of rhizome on 1st age class was the highest, so rhizomes on 1st age class were the main storage part of the underground nutrients. Potential population include daughter ramets, tiller buds, apical rhizome buds and nodal rhizome buds, and the 1st age class tiller buds was dominant, which it was a stable age structure. The vegetative propagative ability of ramets was significantly higher than rhizomes. Comparing the two years of rainfall, the growth of 2nd age class modules was more sensitive to the extreme drought in 2014 than others.