[Objective] Drought stress inhibits the synthesis of photosynthetic pigments in medicinal plants, reduces plant photosynthetic activity and photosynthetic carbon assimilation efficiency, hinders nutrient transport, and seriously affects the quality and quality of medicinal materials; Calcium is an activator of various enzymes in plant physiological activities, and Ca2+, as the second intracellular messenger, is closely related to abiotic stress in plants; Present study investigated that the potential physiological mechanism of exogenous calcium enhances drought resistance and medicinal quality of Platycodon grandiflorus in arid and semi-arid areas tolerance drought stress. [Methods] A pot experiment was set up to explore the effects of exogenous application CaCl2（10 mmol/L） on plant growth, photosynthetic gas-exchange parameters, and quality of medicinal parts in P. grandiflorus seedings under drought stress. [Results](1) Exogenous calcium treatment could significantly increase the root length and dry and fresh biomass of Platycodon grandiflorus under drought stress. (2) Exogenous calcium significantly increased the stomatal aperture, chlorophyll a content, total chlorophyll content, carotenoid content, net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) by 30.28%, 57.67%, 44.44%, 100.33%, 89.53%, 60.00%, and 83.11%, respectively, in P. grandiflorus leaves under drought stress. (3) Exogenous calcium effectively reduced the content malondialdehyde (MDA) and hydrogen peroxide (H2O2) in P. grandiflorus leaves under drought stress, which is significantly reduced by 13.82% and 18.66% compared to drought stress treatment, respectively. Exogenous calcium increased the peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities in P. grandiflorus leaves by 25.43%, 7.90%, and 33.92%, respectively, compared to drought stress treatment, (4) Exogenous calcium alone significant increased medicinal components latycodin-D, polysaccharides, total flavonoids, and free amino acid content in P. grandiflorus roots by 35.34%, 34.87%, 4.19% and 6.52%, respectively. Compared with drought stress treatment, the content of latycodin-D, polysaccharides, total flavonoids and free amino acid were significantly increased by 10.94%, 7.53%, 6.07%, and 5.78% under exogenous calcium treatment, respectively. (5) Exogenous calcium increased the soluble protein content in the roots, and the mineral element content in shoot and root of P. grandifloras under drought stress. [Conclusion] Spraying 10 mmol/L CaCl2 enhanced the protective effect of antioxidant systems in P. grandifloras leaves under drought conditions, which increased the photosynthetic pigment content and photosynthetic performance through osmotic regulation and synergistically enhanced the accumulation of secondary metabolites. At the same time，exogenous CaCl2 enhanced the accumulation of secondary metabolites and mineral element and improved the quality of medicinal parts, resulting in alleviation of drought damage to P. grandifloras seedlings.