Abstract: Experiments of American ginseng’s transpiration under different environmental conditions were carried out from 1997 to 1998 at Jinzhai County，Anhui Province．The results show that the American ginseng’s transpiration rate and stomatal conductance are affected obviously by the change of environmental temperature and humidity American ginseng’s plant growth has good relationships with the daily changes of the transpiration rate and stomatal conductance The transpiration rate and stomatal conductance of healthy plants are higher than those of weak plants．and also their stomatal self-controlling abilities are better than those of weak ones．At a sunny day，under 17．5％ ，25．8％ ，and 35．4％ of the shed’s light transmission rate， the daily changing patterns of American ginseng’s transpiration rate are different，the maximum value of transpiration rate respectively appears at different times，they were“before noon”，“at noon”and “after noon ”． The main factors which influenced American ginseng’s transpiration rate are stomatal conductance and air temperature．