To explore the responses of photosynthesis in leaves of Lonicera japonica to gradually increasing soil drought stress and the quantitative relationships between photosynthesis and soil moisture, we selected threeyearold L. japonica grown on Yimeng Mountain as the experimental material. The response characteristics of photosynthesis, chlorophyll fluorescence and antioxidant enzyme activities in leaves of L. japanica to soil water were measured and analyzed. The results showed that: (1) When the RSWC was in the range of 29.7%-79.6%, P_n and T_r decreased following with the decreasing of intercellular CO₂ concentration (C_i) gradually, indicating that the reduction of P_n was mainly caused by stomatal limitation. While nonphotochemical quenching (NPQ), antioxidase activity increased, indicating that with decreasing RSWC, the redundant excitation energies in PSⅡ were removed by thermal dissipation in leaves of L. japanica, and the antioxidant enzyme activities were improved to scavenge the excess ROS. (2) When the water drought stress was in the range of 11.4%-29.7%, P_n decreased obviously with C_i increasing obviously and L_s decreasing, indicating the limiting factor causing the reduction of P_n was nonstomatal limitation. The maximal photochemical efficiency of PSⅡin the dark (F_v/F_m), actual photochemical efficiency of PSⅡ in the light (Φ_PSⅡ), electron transport rate (ETR), photochemical quenching (qP) and NPQ decreased, and minimal fluorescence (F_o) increased obviously, indicating that the PSⅡ was damaged and the photosynthetic electron transport was inhibited. Antioxidase activities decreased, and content of malondialdehyde (MDA) increased significantly, indicating that the activities of the antioxidant enzymes declined and the cell membrane was destroyed. (3) When the RSWC was 11.4%, P_n was about zero, and plant wilted, the photosynthetic mechanism was damaged mostly in this water range. In conclusion, the three critical moisture thresholds of plant normal growth and rewatering (RSWC_SLNSL=29.7%, RSWC_Pn≈0=RSWC_wilting=11.4%) was clarified, which provided an experimental basis for the research on the mechanism of photosynthetic efficiency in leaves of L. japonica to severe drought and rewatering.