Abstract: Using sweet potato cultivars Xuezhou18 and Wan84-559 as materials, changes of photosynthesis and chlorophyll fluorescence parameters were measured. Under water stress, The decrement of contents of chlorophyll , PSⅡprimary photochemical efficiency（Fv/Fm）and photochemical quenching coefficient (qP) were less; increment of non-photochemical quenching coefficient（qN）were less in Xuezhou18. The above results suggested that damage of photosynthetic apparatus were lighter; more light energy absorbed by Xuezhou18 was converted into chemical energy and less light energy was dissipated through thermal energy.