An efficiency purplish blue phosphor Ca3MgSi2O8:Ce3+ has been synthesized. The emission and excitation spectra of Ca3MgSi2O8:Ce3+ under 260 nm and 360 nm excitations show that they have their common broad band emission characters, but the maximums and the band widths of the emission spectra are different. The excitation spectra of Ce3+ 350 nm emission and 460 nm emission clearly show that there are remarkable differences. These results indicate that there are two kinds of Ce3+ emission centers in the host of Ca3MgSi2O8. According the analysis of the crystal structure and the Van Uitert's empirical equation, we have a conclusion that two centers occupy two kinds of octacoordinated Ca sites, respectively.