| Field water stress during the blooming period was conducted to assess drought resistant capacity and partition clahierarchy of 28 varieties of cotton by drought resistance coefficient.The results showed that cotton varieties under drought stress during the blooming period, indexes responded variously.Chlorophyll, net photosynthetic rate, stomatal conductance, water vapor pressure deficit changed more apparently.The material could be divided into four major categories, by RI value clustering analysis. The first (Ⅰ) type for high class type varieties were C1470, ND359-5, Xinpao 1, Xinluzhong 39 in 18 varieties. The second (Ⅱ) class for the type of resistance included Tianhe 995,Jizha 81,Dalingmian,TM-1, Tashigan 7. The third (Ⅲ) for sensitive was Xinluzao 1, Xinshi K7, Lumian 28. The fourth (Ⅳ) for highly sensitive was Xinluzao 26 earlier,The mathematical evaluation model was established as D=-1.496+0.775Ci+0.160Gs-0.020VPD+0.719Pn+0.799Tr- 0.241WUE+0.663Chl（R2=0.996）,and the evaluation accuracy of the equation was higher than 97.55%. Seven indexes closely related to the chilling tolerance, Ci、 Gs、VPD、A、Tr、WUE and Chl. |