| To study the relationship between the cold tolerance and the physiological characters of winter rape root, an experiment was conducted to analyze the changes of the dry matter, the water content, the soluble protein and the enzymatic activity of the roots of six different cold-tolerant cultivars. It also analyzed the correlation between the winter survival rate and other indexes, and used six significant indexes to get the cluster analysis of the materials. The results showed that, before cooling, the correlation was not significant between winter survival rate and other indexes; but after cooling, the survival rate was most significantly positively correlated with soluble protein and SOD, significantly positively correlated with POD and APX, positively correlated with diameter of roots, root-shoot ratio and CAT activity, while negatively correlated with water content. According to the cluster analysis results, the test materials can be divided into three categories, 1: 07-G01, Tianyou 2 and Tianyou 4, weak cold-tolerant varieties; 2: Shangdang and 74-1, general cold-tolerant varieties; 3: Longyou 6, strong cold-tolerant varieties. So it can be deduced that the bigger the diameter and root-shoot ratio, the higher the winter survival rate; and the higher the SOD, POD, CAT and APX enzymatic activity, the stronger the cold tolerance of the winter rape. |