Abstract: We aimed to further investigate the relationships between the localization of calcium and Ca²⁺-ATPase and the resistance capacity of Puccinellia tenuiflora against saline-alkali stress. We analyzed ultracytochemical localization of calcium and Ca²⁺-ATPase in the root of P. tenuiflora under NaHCO₃ stress by potassium pyroantimonate precipitation and a lead-phosphate precipitation technique, respectively. In the normal condition, calcium antimonate precipitation deposits were low in cytoplasm and mainly concentrated within the plasma membrane and vacuoles in the root hair zone. Ca²⁺-ATPase had a certain activity and mainly localized in the plasma membrane and tonoplasts. Moreover, under 0.448% NaHCO₃ stress, the distribution of Ca²⁺ precipitation particles increased in the cytoplasm, decreased in the vacuole, and mainly concentrated near tonoplasts. Meanwhile, the activity of Ca²⁺-ATPase was significantly increased in the plasma membrane and tonoplasts. Furthermore, under 1.054% NaHCO₃, Ca²⁺ precipitation particles continued to increase in the cytoplasm but were absent in the vacuole. The activity of Ca²⁺-ATPase was also reduced. All these results highlight that the changes in Ca2+ localization and Ca²⁺-ATPase activity play important roles in P. tenuiflora resistance to saline-alkali stress.