Objective To evaluate the dynamic characteristics of serum complement C1q, C3 and C4 levels in stroke patients over 85 years of age, and to analyze the effects of these indicators on the prognosis of cardiovascular events, and to explore its influencing factors. Methods A total of 320 stroke (AIS) patients admitted to our hospital from April 2017 to October 2020 were selected. Then, according to the prognosis of cardiovascular events (cardiovascular events and death, cardiovascular events but not fatal, no cardiovascular events), they were divided into 3 groups. At the same time, the serum of outpatients in the hospital was selected as a control. During treatment, 3 days after treatment, and 7 days after treatment, serum complement C1q, C3 and C4 levels were evaluated. The dynamic changes of serum complement C1q, C3 and C4 levels were determined by enzyme-linked immunosorbent assay. Results During the treatment, the levels of complement C1q, C3 and C4 showed a gradual decrease in 3 days after treatment and 7 days after treatment. Cardiovascular events occurred and died, and cardiovascular events occurred but not fatal. In the three groups of patients without cardiovascular events, serum complement C1q, C3 and C4 levels were significantly higher than those of the normal population. The levels of complement C1q, C3 and C4 in the cardiovascular event and fatal group were significantly higher than those in the cardiovascular event but not fatal group, and the complement C1q, C3 and C4 levels in the cardiovascular event but not fatal group were significantly higher than those in the non-cardiovascular event group , The differences between the two groups were statistically significant (P<0.05). Logistic regression analysis showed that the levels of complement C1q, C3 and C4 at the two time points after treatment can be used as independent factors influencing the prognosis of cardiovascular events (increased levels are risk factors). At the same time, the decreasing trend of complement level is a protective factor for the prognosis of adverse cardiovascular events. Conclusion Elevated serum levels of complement C1q, C3 and C4 in stroke patients over 85 years of age indicate a poor prognosis for cardiovascular events. Dynamic monitoring of serum complement C1q, C3 and C4 levels is of great significance to improve the prognosis of patients.