Abstract: The response of invasive plant Wedelia trilobata to two different nitrogen forms (NH+4/NO-3) were investigated. The results showed that (1) W.trilobata had significantly larger biomass under the condition of the whole ammonium nutrition than under the condition of the whole nitrate nutrition; (2) Whether W.trilobata under the condition of the whole ammonium nutrition or nitrate nutrition, its total biomass and chlorophyll content (SPAD) was significantly higher than the native plant species Wedelia chinensis; (3) Under the condition of whole ammonium nutrition, free amino acid in roots of W.trilobata increased significantly compared to W.chinensis, whereas under the condition of the whole nitrate nutrition the activity of nitrate reductase in both roots and leaves of W.trilobata also increased significantly but its nitrate accumulation decreased significantly compared to W.chinensis. It was concluded that W.trilobata might be of a plant absorbing NH+4-N preferentially. Compared to the native species, W.trilobata had higher ability of ammonium assimilation and tolerance, and nitrate deoxidization, and also had stronger ability of adaptation to the extreme environment, which might be one of the important mechanisms why W.trilobata became invasive. It was implied that the soil habitats where NH+4-N was dominant might be vulnerable to be invaded by invasive species. This might be a crucial change of invasive plants during the process of settlement and spread.