The long-term arid climate in Xinjiang poses a major challenge to sustainable jujube production. In this study, we systematically evaluated the impacts of deficit irrigation (DI) by comparing a full irrigation control (CK) with six DI treatments-mild DI (75% CK) and severe DI (50% CK) water deficits applied during either flowering + fruit setting or fruit enlargement stages. The key findings demonstrate that flowering + fruit setting DI effectively balances water conservation with productivity. Mild DI (75% CK) during flowering + fruit setting reduced irrigation by 72 mm while maintaining near-optimal photosynthesis (95% recovery post-rewatering) and significantly improving fruit quality (5.49-10.28% higher sugar content, 3.40-5.06% larger fruit volume), despite a moderate 4.22-11.36% yield reduction. In contrast, severe DI caused irreversible physiological stress (only 75% photosynthetic recovery), and fruit-enlargement-stage DI uniformly compromised both yield and fruit size. An economic analysis confirmed flowering + fruit setting mild DI as optimal, generating 17,139-20,550 RMBha-1 profit through enhanced water use efficiency (WUE) and premium-quality fruit production. PLS-PM validation revealed that targeted flowering + fruit setting water deficit suppresses vegetative overgrowth while optimizing source-sink relationships, achieving a 23-31% WUE improvement without sacrificing marketable yield. Thus, mild DI during flowering + fruit setting is a climate-smart irrigation strategy for Xinjiang's jujube industry, resolving water scarcity challenges with economic viability.