Three-year-old seedlings of Ziziphus jujuba var. spinosus, a dominant shrub in shell ridge island of China's Yellow River Delta, were used as experimental materials. A series of soil water content in sand formed from seashells were simulated by artificial feeding firstly and then plant transpiring. Light responses of photosynthesis and chlorophyll fluorescence parameters in leaves of Z. jujuba var. spinosus under series water content were measured with CIRAS-2 portable photosynthesis system and FMS-2 portable fluorescence system, respectively. The threshold effects of the main photosynthetic and physiological parameters in leaves of Z. jujuba var. spinosus to soil water and their response relationships were elucidated, and the soil water availability on Z. jujuba var. spinosus leaves' photosynthesis was studied. The results showed that: (1) The net photosynthetic rate (Pn), transpiration rate (Tr) and water use efficiency (WUE) in leaves of Z. jujuba var. spinosus first increased and then decreased with the soil water increasing, while Tr was more sensitive to soil water variation than Pn, thus causing WUE at a higher level. (2) The main reason of Pn declining changed from stomatal limitation to non-stomatal limitation in leaves of Z. jujuba var. spinosus when soil relative water content (Wr) reduced to 25%, Pn was dominated by stomatal limitation when Wr > 25%, and non-stomatal limitation when Wr < 25%, meanwhile photosynthetic apparatus was damaged irreversibly. (3) The maximum net photosynthetic rate, dark respiration rate, apparent quantum yield (AQY) and light saturation point in leaves of Z. jujuba var. spinosus first increased and then decreased, while light compensation point, photo-inhibition term (β) and photo-saturation term first decreased and then increased with the soil water increasing. The Pn light response parameters above all reached the optimum levels when Wr varied from 58% to 76%, meanwhile the photosynthetic activity was higher. (4) The potential photochemical efficiency (Fv/Fm) and actual photochemical efficiency of Z. jujuba var. spinosus first increased and then decreased with the soil water increasing, the photochemical transformation efficiency of PSⅡ reaction center reached maximum when Wr was 80%. Non-photochemical quenching coefficient (NPQ) increased gradually with the aggravation of drought or waterlogging stress when Wr varied from 80% to 30% or from 80% to 95%, Z. jujuba var. spinosus PSⅡ had strong ability of heat dissipation and could prevent photosynthetic apparatus from damage by dissipating excessive light energy. AQY and Fv/Fm decreased rapidly and β increased rapidly when Wr < 30%, photo-inhibition occurred in Z. jujuba var. spinosus leaves significantly. NPQ decreased rapidly and initial fluorescence increased rapidly when Wr < 25%, Z. jujuba var. spinosus PSⅡ was damaged irreversibly. (5) 11%-25% of Wr was low productivity and low WUE for Z. jujuba var. spinosus, 25%-58% was middle productivity and middle WUE, 58%-80% was high productivity and high WUE, 80%-95% was middle productivity and low WUE. In summary, the photosynthesis of Z. jujuba var. spinosus had great physiological adaptability and plasticity to soil water stress in sand formed from seashells. The photosynthetic and physiological activity of Z. jujuba var. spinosus maintained at a relatively high level when Wr was between 58% and 80%, meanwhile Z. jujuba var. spinosus seedling could grow well, and the soil water maximum deficit level allowed in sand habitat for Z. jujuba var. spinosus occurred when Wr was 25%.