Abstract: Based on the results of pot screening,the physiological effects of synergism mixture of glyphosate-ammonium and fluroxypr-mepthyl(4∶ 1,the quanlity prorportions of effective ingredients)against Alternanthera philoxeroider were studied, including net photosynthate,stomatal conductance,intercellular CO2 concentration and content of malondialdehyde and so on,using glyphosate-ammonium and fluroxypr-mepthyl as controls.The results indicated that the actual inhibition ratio and the theoretical inhibition ratio of net photosynthate and stomatal conductance of glyphosate-ammonium and fluroxypr-mepthyl(4∶ 1)mixture against Alternanthera philoxeroider were from 80% to 100%, and those of intercellular CO2 concentration, content of chlorophyll and malondialdehyde were above more than 110%, and strong synergism.The mixture has valuable to deeply process.