Abstract: The branches of Populus X xiaozhuanica cv. ‘popularis' are induced byrare-earth and Streptomyces jingyanesis 5406(three concentrations of 100,500 and 1000ppm in both inducers),then inoculated with Dothiorella gregaria. After challenged inoculation,the incidence of disease and disease index dropped with a reduction of 60%～70% and 29.1～73.9 for the formor and 63.3%～70% and 51,5%～65.2% for the latter respectively. The mechanism of resistance to canker disease is a series of physiological changes takingplace in the bark of branches after induction. The activity of superoxide reached the maximum after 72～96 hours and then dropped gradually and tended to be stable,the activity of SOD in the induced branches are higher than that in the control ones;the respiration came tothe maximum after 48 hours and got weak after 96 hours when disease is going on the totalprotein of induced branches increased by 2.7～5.4 times while that of the control only 1.9 times,The changes above are related to the concentration of inducers with the larger theconcertration the better the effect.