Study on the relationship between plant individual and population is of great importance to explore plant adaptation strategies and to understand the mechanisms of plant invasion. However, most studies focused on the growth trade-off of plant response to density change under normal temperature treatment. There is a lack of understanding on the regulation mechanism of plant density restriction under increasing temperature treatment, and whether the regulation law of response to density change alters under normal temperature and warming treatment. In this study, taking Alternanthera philoxeroides as the focus species, the relationship between density restriction and A. philoxeroides, and the regulation law of density restriction between aboveground and underground parts under the background of global warming were studied by using two-factor experimental design of density (1, 5, 9 plants/pot, 37, 186, 335 plants/m²) and temperature (normal temperature, increasing temperature). The results showed that:(1) There was a significantly positive correlation between the characteristics of aboveground components and temperature (P<0.05), and there was a significant density dependence on the characteristics and specific leaf area of aboveground components (P<0.05). Temperature, population density and their interaction had no significant effect on underground index (P>0.05). (2) With the increase of density, the root biomass allocation ratio increased, while the average biomass and stem biomass allocation ratio decreased under two temperatures. The allocation ratio of leaf biomass remained constant at different densities. (3) The allometric index γ of biomass-density was used to measure the regulation of population density. Under normal temperature treatment, we found that γ_leaf (-1.685) < γ_above-ground(-1.612) < γ_stem (-1.605) < γ _individual (-1.558) < γ_root(-1.524). Regulation intensity restricted by density was in the following order:leaf > aboveground > stem > individual > root. Under warming treatment, we found that γ_stem (-2.075) < γ_above-ground (-2.038) < γ_individual(-1.982) < γ_leaf (-1.933) < γ_root (-1.800). The order of regulation intensity restricted by density was stem > aboveground > individual > leaf > root. The density regulation of the aboveground components of A. philoxeroides population is stronger than that of the underground ones. That's to say, whether warming or not, the competitiveness of underground resources of A. philoxeroides population increases with the increase of density, while the competitiveness of aboveground resources decreases with the increase of density. The regulation ability of the upper part of A. philoxeroides is stronger than that of underground part. Under normal temperature treatment, leaves are more restricted by density, while stems are most restricted by density under warming treatment. The competition for aboveground resources is dominant for A. philoxeroides.