Abstract: In order to study the cold resistance mechanism of Poplar, taking annual dormancy branches of 5 clones and 3 control clones as experimental materials. Physiological indexes were measured after stress treatment at -15, -20, -25, -30 and -35 ℃ for 24 h, and the cold resistance of 8 species of Populus deltoids clones was quantitatively evaluated by membership function method. Results showed that LT₅₀, SOD activity, POD activity, soluble protein content and mass concentration of MDA can be used to quantitatively evaluate the cold resistance of 8 tested clones. There were obvious differences among the clones of the ability of cold resistance. The cold resistance of 8 species of Poplar deltoids clones from strong to weak was Nankangyang, '08H1-6', '03S4-1', '08H11-11', Shanlin No.3, '08H2-16', 69 Yang, '08H4-5'. The cold resistance of '08H1-6', '03S4-1' and '08H11-11' were between Nankangyang and Shanlin No.3, which can provide reference for the popularization of new varieties with excellent cold resistance.