With rapeseed roots of four different cold hardiness under continuously cool treatment (4 ℃ 24 h,0 ℃ 24 h,-3 ℃ 24 h,-6 ℃ 24 h,-9 ℃ 24 h,-15 ℃ 24 h,-21 ℃ 24 h) in the low temperature test boxes,testing the antioxidant enzymes activities (POD and CAT) and the POD isozymes electrophoresis and morphological variation characteristics of rape seedlings before and after the frozen treatments.To explore the correlation for changes of antioxidant enzyme activities at low temperatures and the ice formation in root cells of winter rapeseed and antifreeze mechanism of the winter rapeseed root.The result showed that:(1)The varieties of weak frost resistance rapeseed (‘Longyou 7’ and Vision) in the low temperature appeared a large number of water damage was on the surface of leaves,then the leaf blade atrophied until withered,root appeared water softening until dry death;strong frost resistance varieties (‘Longyou 6’ and ‘Longyou 8’) in the frozen did not produce water damage,or water damage was less,and the damage of its root was slighter.(2)Under continuously cool treatment,POD and CAT activities of the weak frost resistance rapeseed roots in early cooling had large changes,and then kept constant,indicating that the cells of roots had completely froze;POD and CAT activities of strong frost resistance rapeseed root in early cooling had small changes,which greatly increased in later period,indicating that the cells of roots remained solution state;The analysis of POD isozyme also reflected a similar change.Research showed that there were some correlations between changes of antioxidant enzyme activities of winter rapeseed root and the frozen stage of root cells in low temperature.Cell ice usually caused plant fatal damage,which stated that the key that strong cold hardiness rapeseed can winter safely was that avoiding intracellular ice formation,and the lower freezing temperature of its cells is,the stronger the cold hardiness of them is.