Objective To study the association of maternal calcium supplementation and dietary calcium intake with the preterm birth so that to provide scientific basis for effective intervention of preterm birth. Methods Normal pregnant women who were followed up all through to childbirth in Gansu Provincial Maternity and Child Care Hospital were selected. Multivariate logistic regression was used to evaluate the associ-ation of calcium supplementation and intake with preterm birth. Results After confounding factors were adjus-ted, pregnant women who took calcium supplement for more than 3 months before and/or during pregnancy had the risk of preterm birth reduced by 14% which was dose-responding ( OR=0. 86, 95% CI=0. 77-0. 96, P<0. 05). Through stratifying by trimesters of pregnancy, it was found that calcium supplement in the third trimes-ter was a protective factor for preterm birth and especially significant in early and very early pregnancy ( OR=0. 75, 95% CI=0. 62-0. 92, P<0. 05). Through stratifying by dietary calcium intake, pregnant women who took dietary calcium more than 465. 55 mg/d had the risk of preterm birth significantly reduced which was shown by the reduction of preterm birth of different degrees, controlled preterm labor and spontaneous premature dilivery (OR=0. 66, 95% CI=0. 53-0. 82, P<0. 05). Conclusion Appropriate calcium supplementation or dietary calcium intake before and during pregnancy can reduce the risk of preterm birth, which is especially sig-nificant in late pregnancy.