Calligonum mongolicum is one of the most important sand binding plants distributed in desert areas of northern China. The expansion of Calligonum mongolicum population plays an important role for ecological restoration in the transition zone between oasis and desert. However, no related information is available. Field investigations have been performed at four different habitats including fixed dune, lowland, windward and leeward of semi-mobile dune in the desert-oasis ecotone to examine the expansion of Calligonum mongolicum population. Reproduction pattern, growth characteristics, the relationship between population quantity and age, population expansion range and expansion rate of Calligonum mongolicum were identified. The results demonstrated: (1) Calligonum mongolicum grows mainly through a sexual reproduction in the sandy environments. The density percent of ramets in fixed dune，lowland，windward and leeward of semi-mobile dune were 35%,45%,2%, and 9%, respectively; the density percent of seedlings in fixed dune，lowland，windward and leeward of semi-mobile dune were 65%,55%,98%, and 91%. (2) Calligonum mongolicum population is an increasing population in different habitats. (3) The expansion range and average expansion rate of vegetative reproduction were 1-5m and 0.67m/a, 1-8m and 0.64m/a, 0-2m and 0.15m/a, 1-4m and 0.41m/a in fixed dune, windward and leeward of semi-mobile dune, lowland, respectively. Meanwhile, the density and expansion rate of Calligonum mongolicum population decreases with the increase of age. (4) The invasion of Calligonum mongolicum population to a new habitat starts at the seedling stage with sexual reproduction, and then rapidly expands to a large area through the ramets-vegetative reproduction. The vegetative reproduction drives the expanding of Calligonum mongolicum population persistently.