Abstract: 【Objective】 This study aimed to investigate the synergistic pathogenic mechanism of coinfection with alfalfa mosaic virus（AMV） and white clover mosaic virus（WCMV）（3∶1） in Nicotiana benthamiana.【Method】 The activities of four disease-resistant enzymes in leaves were determined at 2,4,6,8,and 10 days after co-inoculation of AMV+WCMV（3∶1） using a biochemical method,with individual friction inoculation by AMV,WCMV,and PBS buffer solution（pH 7. 0） as the control.【Result】 The results demonstrated that the activities of POD,PPO,PAL,and CAT enzymes in the leaves,which were treated with co-inoculation of AMV+WCMV（3∶1）,were significantly increased compared to those inoculated with AMV,WCMV or the PBS buffer control alone（P＜0. 01）. The stress response rates varied among the four enzymes.【Conclusion】 Co-infection of AMV+WCMV（3∶1） aggravated the occurrence of viral diseases and significantly enhanced the activities of 4 enzymes related to disease resistance（i. e.,POD,PAL,PPO,and CAT） in the host plant.