Through pot experiment and physiological-biochemical analysis, the study showed that the electric conductivities of Conyza canadensis collected from heavy Cu pollution (I), light Cu pollution (II) and control (III) sites were enhanced, while the chlorophyll (a + b) contents were reduced with increasing Cu concentration. The protein and proline contents in I were increased at first and then reduced, but those in II and III were reduced with increasing Cu concentration. The activities of SOD, POD and CAT were intensified under Cu stresses. When the Cu concentration was 1 200 mg x kg(-1), their activities in I, II and III were increased 194.1%, 206.2% and 118.6%, 170.1%, 182.9% and 111.3%, and 115.1%, 155.4% and 107.3%, respectively, in comparing with the control, which illustrated that the tolerance of Conyza canadensis was in order of heavy Cu pollution site > light Cu pollution site > control site, and the three ecotypes showed distinct differences in tolerance.