Ca9Al(PO4)7: Eu2+ blue emitting phosphor was synthesized by high temperature solid state method. Luminescence, concentration quenching and thermal stability of Ca9Al(PO4)7: Eu2+ were investigated. Excitation spectrum of Ca9Al(PO4)7: Eu2+ extended from 200 nm to 350 nm. Under an ultraviolet excitation, Ca9Al(PO4)7: Eu2+ showed a broad emission band with a maximum at 445 nm, which corresponded to 4f65d1→4f7 transition of Eu2+. Emission intensities of Ca9Al(PO4)7: Eu2+ were influenced by Eu2+ concentration, and they enhanced with increasing Eu2+ concentration, and reached a maximum value at 0.01 Eu2+, then decreased with further increasing Eu2+ concentration because of concentration quenching effect. The concentration quenching mechanism was verified to be dipole-dipole interaction. According to crystal structure data, critical distance can be obtained to be 2.297 nm. The emission intensity of Ca9Al(PO4)7: Eu2+ as a function of temperature was explored. When temperature turned up to 150 ℃, the emission intensity of Ca9Al(PO4)7: Eu2+ was 81.0% of the initial value at 25 ℃, and the corresponding activation energy was calculated to be 0.268 eV, which could prove the thermal stability of Ca9Al(PO4)7: Eu2+.