Ca5MgSi3O12:Eu2+, Dy3+ was synthesized by solid-state reaction. The luminescence center related to the oxygen vacancies existed in the host matrix. Comparing the fluorescence and phosphorescence properties of samples synthesized under different air condiction, we find that the oxygen vacancies played an important role in the fluorescence and phosphorescence properties. Oxygen vacancies can transfer its energy to the luminescence center. Thermoluminescence spectra were used to characterize the effect of oxygen vacancies on the phosphorescence properties. Ca5MgSi3O12:Eu2+,Dy3+ has a great potential to become a promising candidate to be used as long-lasting phosphors.