Abstract: 【Objective】 This study explored the effects of foliar spraying of amino acid calcium （ACa） and nano calcium carbonate （NCa） on the physiological responses of tea plants under various abiotic stresses， as well as the specific mechanisms involved， comprehensively assessed their synergistic potential in terms of stress resistance and fluoride reduction， with the aim of providing theoretical basis for the development of tea tree-specific foliar calcium fertilizers with both stress resistance and fluoride reduction functions. 【Method】 One-year-old cuttings of Camellia sinensis cv. Xinyang No. 10 were used as experimental materials. Three treatments were applied： foliar spraying with pure water （CK）， ACa （diluted 4000 times）， and NCa （diluted 10000 times）. After two weeks of consecutive foliar applications， the plants were subjected to low temperature （-6 ℃）， high temperature （42 ℃）， and drought stress， followed by exogenous fluoride treatment. Leaf biomass， calcium and fluoride contents， reactive oxygen species contents， antioxidant enzyme activities， and osmoregulatory substances were measured， and principal component analysis was used to comprehensively evaluate the physiological response patterns. 【Result】 Compared with CK， both calcium treatments effectively alleviated stress damage of tea plants， significantly increasing leaf fresh weight and dry weight （P<0.05， the same below）. The leaf fresh weight of the ACa treatment increased by 76.1% under low temperature stress， while that of the NCa treatment increased by 54.9% under high temperature stress. Calcium treatment increased leaf calcium content by 1.2-1.8 times and reduced fluoride content by 18.4%-26.7%， with a extremely significant negative correlation between leaf calcium and fluoride contents （r=-0.984）. Both calcium treatments significantly reduced the contents of superoxide anion， H₂O₂， and MDA in leaves under all three stresses. Under high temperature stress， the scavenging effect of NCa on reactive oxygen species was slightly better than that of ACa； under low temperature and drought stresses， ACa exhibited stronger inhibitory effect. Calcium treatment significantly enhanced the activities of antioxidant enzymes under the three stresses， sho-wing calcium source specificity： NCa treatment was more effective in activating POD， with POD activity increases of 290.5%， 68.8%， and 186.6% under low temperature， high temperature， and drought stresses respectively. ACa treatment was more effective in enhancing CAT activity， with increases of 62.5%， 245.2%， and 162.4% respectively. ACa treatment promoted the accumulation of proline， soluble sugar， and soluble protein better than NCa treatment under all three stresses. Principal component analysis indicated that foliar calcium application reshaped the physiological state of tea plants， presenting a dual-effect pattern of enhanced stress tolerance and reduced toxicity. 【Conclusion】 Foliar calcium application improves the stress tolerance of tea plants by coordinately activating the antioxidant enzyme system and enhan-cing osmoregulatory capacity， while significantly reducing leaf fluoride content. The regulatory advantages of ACa and NCa are distinctly stress-dependent. The application of both types of calcium sources can serve as effective agronomic measures for tea tree stress-resistant cultivation and the safe production of tea with reduced fluoride content.