Abstract: Poplar canker disease is newly discovered disease which occurred on the domestic widely planted varieties of Populus×euramericana, both the bacterium Lonsdalea quercina and the fungus Fusarium solani isolated from the poplar induced the symptom on cultivar of Populus×euramericana when conducting inoculation in field and in greenhouse, but more typical symptoms induced when inoculated with L. quercina. The role of F. solani playing in occurrence of Populus×euramericana canker disease is unclear. In order to clarify the relationship between the two kinds of micro-organisms in the process of Populus×euramericana canker disease, dual culture, inoculation experiment and field investigations were conducted, and the resulting data were analyzed by using SPSS software. The results indicated that: antagonistic relations did not exist between L. quercina and F. solani, and the pearson correlation coefficient that the lesion induced by mixed inoculated with L. quercina and F. solani, and by inoculation separately with the two, were 0.9 and 0.8 respectively. The higher correlation coefficient for the disease occurrence suggested that L. quercina played the major pathogenic role. F. solani with lower virulence usually appeared in late stage of poplar canker disease, played an aggravating role for occurrence of poplar canker disease.