Maize (Zea mays L.) is one of the most important crops worldwide. However, low temperature limits seed germination and seedling growth of maize, which can in turn affect grain yield. The calcium ion (Ca²⁺) is the second messenger involved in the response to environmental-stimuli-induced signal transduction networks. The underlying physiological mechanisms related to the effects of exogenous Ca²⁺ treatment of different maize cultivars under low temperature are unclear. We selected two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. Y478, for studying the effects of Ca²⁺ on seed germination, photosynthesis, antioxidant enzymes and the osmotic regulation of seedling resistance to low temperature. The optimal concentration of CaCl₂ was 80 mmol L^-1, which significantly improved the germination percentage at temperatures <10°C. Application of CaCl₂ at this concentration under cold stress mitigated the degree of membrane injury and improved the antioxidant enzyme system through reduced relative electrolyte conductivity and malondialdehyde content, increased the soluble protein content, and enhanced superoxide dismutase and peroxidase activity. CaCl₂ also significantly increased chlorophyll fluorescence indicators (F_v/F_o, F_v/F_m) and the photosynthetic rate. We conclude that exogenous CaCl₂ at a concentration of 80 mmol L^-1 protects the function and structure of the membrane and photosystems, improves antioxidant enzyme activity and increases osmotic regulatory substances under cold stress. These results improve our understanding of the mechanisms of Ca²⁺ and contribute to the development of cold-tolerant maize varieties.