Abstract: In order to clarify morphological and physiological responses of Ammopiptanthus seedlings on soil moisture , eight-month old seedlings of Ammopiptanthus were cultivated for three months in four kinds of soil conditions along 1.90%-2.19%, 3.40%-3.59%, 5.40%-5.59% and 8.20%-8.39%. With vernier caliper, ruler, LI-6400xt photosynthetic apparatus and 6400XT-40 fluorescent leaf chamber, their growth and photosynthetic fluorescence parameters were measured and analyzed respectively. The results showed that the soil water content had a great significant effect on growth and photosynthetic fluorescence parameters of ammopiptanthus seedlings. When the soil water content was lower than 3.40%, the growth of Ammopiptanthus seedlings were seriously inhibited, and some of their leaves changed into yellow or withered. Simultaneously, with the soil water stress gradually intensified, all of the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate(Tr) of Ammopiptanthus seedlings gradually reduced, and its intercellular CO2 molar concentration (Ci) first decreased and then increased. And it also implied that the soil water stress made the stomatal limitation turned into nonstomatal limitation, which resulted in the decease of leaf photosynthetic capacity. Furthermore, as the duress of soil moisture exacerbated, the determination of chlorophyll-fluorescence parameters revealed that the PSII maximal photochemical efficiency (Fv/Fm), the Photo-synthetic electron transport (ETR) and the photochemical quenching coefficient (qP) reduced, the steady-state fluorescence parameters (Fs) intermittent decreased, and the photochemical quenching coefficient qN and NPQ increased. In addition, the damage of PSII brought inactivation of photosynthesis center, decreased both primary capture capacity and assimilation efficiency of light energy, increased light energy consumption by means of heat, and final weakened photosynthesis capacity of Ammopiptanthus seedlings.