Objectives To investigate calcium supplement in pregnancy for prevention of preeclampsia and relevant outcomes. Methods The Cochrane Library, PubMed, EMbase, CBM, WanFang Data, VIP and CNKI databases were searched online to collect randomized controlled trials (RCTs) of calcium supplement in pregnancy for prevention of preeclampsia and relevant outcomes from inception to July 2018. Two reviewers independently screened literature, extracted data and assessed the risk of bias of included studies. Meta-analysis was then performed by RevMan 5.3 software. Results A total of 33 RCTs involving 29 234 subjects were included. The results of meta-analysis showed that: compared with control group, the calcium supplement group was associated with lower preeclampsia (RR=0.48, 95%CI 0.38 to 0.62, P<0.000 01) and gestational hypertension (RR=0.65, 95%CI 0.55 to 0.77,P<0.000 01) incidence. The incidence of premature delivery, intrauterine growth retardation and severe preeclampsia in calcium supplement group was lower than that in placebo group, and the neonatal weight in calcium was higher than that in placebo group. However, there was no significant difference in the pregnancy cycle between the two groups. Conclusions Current evidence shows that calcium supplement is associated with lower risk of preeclampsia and gestational hypertension. Due to limited quality and quantity of the included studies, more high quality studies are required to verify the above conclusion.