This study aims to elucidate vegetative propagation in Phragmites communis, and its role in colonizing active sand dunes. The experiment was conducted in the Horqin Sand Land in Inner Mongolia, northeastern China. Quadrats were established along twenty transects from the dune slack to the windward slope through the ecotone (a transitional zone between the dune slack and the windward slope of active sand dune). Biomass, biomass allocation and relative growth rate (RGR) of P. communis were quantified monthly from May to August in 2007. Our results showed that rhizomes extended towards the active sand dune at a rate of 523.5 ± 20.8 cm per year. The RGR of ramets and rhizomes increased along the gradient from the dune slack to the windward slope. The percentage of rhizome biomass in total biomass increased significantly along the same gradient. The results indicate that P. communis is able to adjust growth strategy according to the environmental conditions. The results also demonstrate that vegetative propagation of rhizomatous grasses significantly contributes to plant encroachment to active sand dunes and plays an important role in the vegetation restoration of dune fields.