Abstract: The phenotypic plasticity in response to different light intensity in the invasive species Alternanthera philoxeroides was studied.The results showed: from full light(100%),60.4%,35.4% to 16.5% full light,branching intensity of A.philoxeroides decreased significantly.Inter-node length and plant total length were the longest under full light and the shortest under low light level.With the decrement of light intensity,the accumulation of total biomass and individual organs’ biomass of A.philoxeroides decreased significantly,and the allocation of individual organs’ biomass differed significantly.The results indicated that light intensity might be the major factor,which affected the survival,maintainability,growth and successful invasion significantly.A.philoxeroides could not extend the population under low light intensity level,which means fewer opportunity of successful invasion into these types of ecosystems.