Abstract：Calcium isotope, one of non-traditional stable isotopes, has been a research hotspot in isotope geochemistry field since the last decade. Calcium isotope ratios are widely measured by TIMS or MC-ICP-MS, and are expressed as δ44/40Ca or δ44/42Ca respectively. Variations of δ44/40Ca in nature are mainly from -2.0‰ to 2.0‰, spanning only a limited range of 4.0‰. The hypotheses of kinetic and equilibrium fractionation can interpret some of calcium isotope fractionation observations, but more work is needed to better understand the fractionation mechanism. Up to now the geological application of calcium isotope includes：(1)Paleoceanography temperature reconstruction based on δ44/40Ca of planktonic foraminifera G. sacculifer；(2) Geochemical cycling of calcium in ocean；(3)Estimation of pCO2 in terms of seawater calcium concentration.