In order to explore the reaction mechanisms underlying plants during the dry-wet alternating soil environment which bring about by intermittent and seasonal drought, the three-leaves stage seedlings of Rheum officinale Baill. were used as experimental materials, a pot experiment was carried out to study its response mechanism under different drought duration (The first drought lasted for 10 days, the second drought lasted for 25 days after rehydration, and the third drought lasted for 40 days after rehydration), different drought gradient (normal water supply, mild, moderate and severe drought) and different rewatering time (1st and 3rd day). The results indicated that drought stresses obviously decreased the aboveground biomass and increased the root-shoot ratio, accompanied with significant decrease of leaf chlorophyll content, gas exchange parameters (Pn, Ci, Gs, E, CE), photosynthetic system performance index (PIabs, PItotal) and fluorescence parameters (Fv/Fo, Fv/Fm, qp). In addition, a large number of QA- was accumulated and the curves of OJIP in phase J and I increased significantly. Slight or moderate drought for 10 days had less inhibitory effect on leaf PSII system with no significant changes including ΦPSⅡ, ETR and Fo. With the drought duration, PSII system was significantly damaged, and the value of NPQ was almost zero after 40 days of severe drought. Rewatering after 10 days of drought, Fv/Fo, Fv/Fm, j-phase, i-phase, Mo, ETR recovered rapidly. Rewatering after 25 days of drought, Pn, Gs, CE, E, Ls and chlorophyll b in leaves showed obvious compensation effects. The Pn, Gs, CE, E, chlorophyll content, most of the fluorescence parameters, j-phase and i-phase of OJIP curve, etc. did not recover to CK level when rewatering after the third drought period lasted 40 days. Under drought stress, the leaf resisted light damage by heat dissipation. With the increase of drought stress and drought duration, the electron transport rate was severely inhibited, the photoprotective mechanism failed, and the reaction center was inactivated. The study found that the photosynthetic and fluorescence parameters recovered quickly under rewatering after short-term drought, showing compensation effect. Under slight or moderate drought stress, the plant that continued to dry for 25 days after rehydration showed stronger drought resistance and recovery ability than those only after 10 days of drought. Long-term and severe drought destroyed the photosynthetic apparatus, the plant did not fully recover its normal physiological function caused by the extremely light and growth inhibition even after rehydration. Thus, suitable drought exercise at seedling stage could enhance the photosynthetic capacity and PSII function, as well as improve drought resistance.