The red long-persistent phosphor CaO: Eu3+ is prepared by a co-precipitation method with further thermal decomposition. The X-ray diffraction analysis shows that the crystal structure of calcium carbonate sample transforms into a single-phase structure and then generates a single-phase calcium oxide structure with the increase of sintering temperature. The excitation spectrum of CaO: Eu3+ shows a broad band around 255 nm, which is attributed to the charge transfer of Eu3+-O2-, and a sharp peak at 393 nm. The emission spectral limes of sample correspond to Eu3+ transitions between 5D and 7FJ (J=0, 2, 3, 4) electron configurations. The red long afterglow is observed at room temperature. A trap level located at 0.69 eV is found by thermolumihnescence measurement, which arises from the fact that Eu3+ is substituted for Ca2+ and enters into the lattice The afterglow luminescence mechanism of sample was discussed according to quantum tunneling.