During range expansion, invasive plants may evolve distinctive traits that make them rapidly occupy the suitable sites at the invasion front, but it is unknown how stand biomass (i.e., biomass production of dense monocultural stands, which may predict invasion speed and impacts) changes during range expansion, and if stand biomass is related to competitive ability. In this study, we examined how competitive ability against common intraspecific competitors and stand biomass when six plants from the same population were grown together change during range expansion, using 27 populations of the invasive Mikania micrantha on Hainan island of China. Competitive ability did not decrease towards the range edge. Stand biomass decreased towards the range edge in 11 L pots with a thick soil layer, but not in 3 L pots with a thin soil layer. Stand biomass was negatively correlated with root-to-shoot ratio in 3 L pots but not in 11 L pots. Stand biomass was unrelated to competitive ability. Our results indicate that edge populations of invasive M. micrantha may have reduced stand-level performance in habitats with thick soil layers. In habitats with shallow soil layers, populations may evolve greater allocation to roots and reduced stand-level performance.