Abstract: In order to study the effects of water deficit and rewatering on soybean seedlings under different air related humidity (RH), the cross pot experiments including four treatments, the two-level soil moisture factor (W/D) and the two-level RH (H/L), were carried to do primary researches on tested material ‘Yudou19’. The controlled temperature and RH were setted in plant growth chamber. The results indicated that, all parameters were conformed to WH > WL > DH > DL. It obviously inferred that, soil moisture was more significant than air humidity by largely affecting plant’s growth. While, by raising RH could only relieve the injuries coursed by drought stress. The stomatal limitations to photosynthesis were dominant under drought stress. Rewatering experiments made all the treatments recovering from the risk of drought, and rewatered experimental groups were finally close to the level of the control groups.