The concentration of calcium is only below sodium and magnesium among metalions, which plays a crucial role in biological processes and the formation of minerals. As analytic accuracy has been increasing, studies of calcium isotopes now become hot focus. Fractionation mechanism and paleoceanographic applications of calcium isotopes in marine settings are perfected with time. Globigerinoides sacculifer is the most promising proxy allied with other proxies of sea surface temperature because its calcium fractionation being sensitive to temperature, with simple formulas and resistant to diagenesis and it is also accessible to test. Those who are not sensitive to temperature in fractionation can be used to recover calcium budget. Inorganic calcium carbonates are promising to evaluate the influences that seepage of methane may exert on paleo-climate.