Abstract：【Objective】In order to clarify the action mechanism of tusite on Duranta repens cv. Gold leaves inoculated with Cuscuta japouica Choisy from the perspective of plant physiology and provide scientific basis for controlling C. japouica. 【Method】The part of physiological indexes of C. japouica and D. repens cv. sprayed by tusite in 3 density（6 mL/L，10 mL/L and 14 mL/L） were measured. 【Result】Within the tested concentrations of this experiment， the activity of SOD and the content of soluble protein were significantly lower than those in control，which are 28.34%， 38.73%， 58.68% and 67.37%， 39.62%， 71.05% of control； The content of soluble sugars and the activities of CAT and POD were obviously higher than those of the controls in tusite on C. japouica. And in D. repens cv. sprayed by tusite， the chlorophyll fluorescence parameters， photosynthetic parameter， the content of soluble protein， the content of soluble sugars and the activities of protective enzymes（SOD， CAT and POD） were significantly rising. The chlorophyll（a and b） content were notably higher in 6 mL/L than controls and the results are 1.53 and 1.35 times of control but no significant difference in 10 mL/L and 14 mL/L. 【Conclusion】The 6% tusite AS have effects by altering metabolism of protein and other biomacromolecule and destroying the balance of protective enzyme in C. japouica. On the contrary， the host plant， D. repens cv.， can prevent injury from tusite through remaining higher level of photosynthesis， increasing the content of soluble protein and keeping the balance of protect enzyme.