Abstract: In order to reveal the effect of foliage applications of KH2PO4 on photosynthesis and chlorophyll content of jujube leaves in flowering and fruit setting period, a field experiment based on single factor randomized block design was carried out in close planting juvenile Junzao orchards in Tarim reclamation area of Xinjiang. There were 3 concentration levels, including 0.6%, 0.3% and 0% (CK) of KH2PO4. The results showed that: foliar spraying potash fertilizer could significantly improve the chlorophyll a and chlorophyll b and total chlorophyll content and net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), but different potassium levels did not change the diurnal variation rules of photosynthetic physiological parameters. During the flowering and fruit setting period of Junzao, the curve of diurnal variation of Pn was unimodal type without obvious ‘midday-depression’ phenomenon. The main reason for decline in Pn was different in a day, which was ‘stomatal factors’ in the morning before 14:00 and non-stomatal factors in noon after 14:00. Potassium could improve stomatal factors effect and reduce the stomatal limitation action. The diurnal variation of Gs and Tr both presented ‘M’ types which performed a good synergistic effect. Meanwhile, foliage K could promote positive correlation between Pn and Ls (stomatal limitation rate), and the same as Pn and WUEi (potential water use efficiency), but reduce the correlation between Pn and WUE (instantaneous water use efficiency). The suitable concentration for KH2PO4 foliage fertilizer was 0.6% within the test range.Keywords: foliar-fertilizer; photosynthetic rate; diurnal variation; chlorophyll; stomatal limitation; efficiency of water application