【Objective】The effects of potassium fertilizer applied to soil at different levels on leaf physiological characteristics，yield and fruit quality were evaluated to determine the optimal application amount of potassium in coastal saline soil.【Method】Potassium fertilizer at 0，125，250 and 375 kg/ha levels was applied to 10-year-old winter jujube trees （Zizyphus jujuba Mill. cv. Dongzao） before bud break and during the fruit expansion period. Under four different treatments of potassium application，leaf enzyme activity，potassium content，osmotic potential，relative turgidity，fruit yield and fruit quality were investigated and analyzed. 【Result】Potassium application significantly increased activities of catalase and peroxidase. Compared to the control，osmotic potentials of jujube leaves treated by 125 kg/ha，250 kg/ha and 375 kg/ha were respectively decreased by 19.8%，36.1% and 38.2% at harvest period and the differences were obvious. In comparison to the control，potassium fertilizer improved relative turgidity and K+/Na+ of leaf，of which，250 kg/ha and 375 kg/ha treatments were significantly better than treatment of 125 kg/ha but statistical analysis demonstrated that no difference was found between them. Also，potassium application increased fruit yield and the highest value of 28050.0 kg/ha occurred in treatment of 250 kg/ha potassium but it was not different from 375 kg/ha treatment. Due to potassium application，fruit quality was improved in ratio of sugar to acid and the best effect appeared in treatment of 375 kg/ha. 【Conclusion】Potassium application at the rate of 250 kg/ha is highly recommended for yellow river delta.