Abstract: After 6, 12, 18 and 24 hours' treatment with 0℃ chilling stress on Chamaecrista rotundifolia, the contents of chlorophyll (chl) decreased by 21.89%, 26.04%, 28.16% and 29.31% than CK(25℃), respectively, dissolubility protein content, H₂O₂ content and ·O^-₂ net generation rate increased with chilling stress time, the scavenging enzymes(SOD) activity increased at earlier stage and then dropped. The treatment of Ca²⁺ fertilizer under chilling stress could significantly decrease the net rate of ·O^-₂ generation, the content of H₂O₂ and the leakage rate of electrolyte, the contents of scavenging enzymes SOD, meanushile, the chlorophyll (chl) content increased. The effect of 0.5 mmol/L CaCl₂ treatment was the best. The results indicated that Ca²⁺ could protect the membrane structure of Chamaecrista rotundifolia under chilling stress.