Abstract: Global warming and biological invasion are the key processes affecting biodiversity and the func‐tions of the ecosystems .Open‐top chamber (OTC) was used in an experiment reported in this paper to study the effects of simulated warming on the flowering phenology and reproductive allocation of Erigeron annuus ,an alien invasive plant species which invaded China many years ago ,is now widely distributed in the country and has caused serious damage .E. annuus flowered from May to September in the OTC and , as compared with the control ,the flowering amplitude of E. annuus individual plants showed a single‐peak curve and had a relatively higher flowering amplitude .Short‐term warming significantly affected the flow‐ering phenology of E. annuus on individual and population levels ,advanced the onset time of flowering and the peak flowering date (p<0.01) and prolonged the flowering duration (p<0.05) .Short‐term war‐ming significantly decreased the leaf biomass and leaf‐weight ratio of the plant and significantly increased its root/leaf ratio (RLR ,p<0.05) .In summary ,short‐term warming significantly advanced the flowering of the invasive plant E. annuus ,prolonged its flowering duration ,and increased its flower number and seed size and quality ,thus enhancing its reproduction investment and invasiveness .