Objective To systematically evaluate the effect of vitamin C supplementation on the mortality of patients with sepsis and septic shock. Methods The Cochrane Library, PubMed, EMbase, Wanfang Data Knowledge Service Platform, China National Knowledge Infrastructure Database and Chinese Science and Technology Periodical Database were searched by computer for randomized controlled trials (RCTs) on the effect of vitamin C on the mortality of patients with sepsis. The retrieval time of each database was from the establishment of the database to January 20, 2022. Two researchers independently screened the literature, extracted data, and evaluated the quality, and then used STATA 16.0 software for meta-analysis. Results A total of 15 RCTs were included, with a total of 2077 patients, including 1041 in the experimental group and 1036 in the control group. The results of literature quality showed that 7 studieswere grade A and 8 studies were grade B, indicating that the overall quality of the included literature was good. The results of meta-analysis showed that compared with the control group, the mortality of patients with sepsis and septic shock in the experimental group were effectively reduced [odds ratio (OR)=0.81, 95% confidential interval (CI) 0.67 - 0.98, P=0.027]. The results of subgroup analysis showed that vitamin C supplementation therapy for more than 4 days could significantly reduce the mortality of the patients with sepsis (OR=0.67, 95%CI 0.49 - 0.90, P=0.008); single treatment could significantly reduce the mortality rate of patients with sepsis (OR=0.50, 95%CI 0.34 - 0.74, P=0.001); vitamin C supplementation can effectively reduce the short-term (≤30 days) mortality of patients with sepsis (OR=0.77, 95%CI 0.63 - 0.96, P=0.017). The funnel plot showed that the included literature was basically symmetrical, and publication bias could not be considered. Conclusions Vitamin C supplementation can effectively reduce the mortality rate of patients with sepsis and septic shock. Vitamin C supplementation treatment course of 4 days or less and single treatment can reduce the mortality rate of patients with sepsis and septic shock, but cannot reduce the long-term (90 days) mortality rate of patients.