Abstract: Using Henan province self-bred Yuyan new varieties Yuyan 6, Yuyan 7 and Yuyan 10 as research subjects, the soil moisture, root morphology and activity, leaf proline and superoxide dismutase（SOD） activity in three critical periods of growth and development（root-extended period, early and late vigorous growth periods） were determined and compared among the three Yuyan new varieties under natural conditions. The results showed that： compared with other sampling periods, in the late vigorous growth stage, the root morphology among the three Yuyan new varieties differed most, the root length, surface and volume of Yuyan 7, Yuyan 6 and Yuyan 10 were in a significantly descending order. The root activity in late vigorous growth stage, leaf proline content when the soil moisture is the lowest and leaf superoxide dismutase in all the three critical periods were all following the pecking order of Yuyan 7>Yuyan 6>Yuyan 10. Therefore, in Henan province tobacco growing areas, the environmental adaptation ability of Yuyan 7 is stronger, which is followed by Yuyan 6, Yuyan 10 has the worst environmental adaptability.

Key words: Yuyan new varieties, root morphology, root activity, proline, SOD