Abstract The site and local structure of activator Eu2+ in phosphor Ca10−x(PO4)6Cl2:xEu2+ is investigated by experiment measurements, first-principle calculations and XAFS simulations. From first-principle calculations, the “local” structure [bond length L(M–O)≤R(M2+)+R(O2−)] of host shows a significant deformation (expansion) when Ca2+ is substituted by Eu2+, and Eu2+ should prefer 6h site to 4f site in the host. The d→f emission of Eu2+ at 4f site should show a longer wavelength than that of Eu2+ at 6h site. The XAFS measurement and simulations suggest that the Eu2+ in our Ca9.9(PO4)6Cl2:0.1Eu2+ sample mainly locates at 6h site. In the emission spectrum, two emission profiles of Ca9.9(PO4)6Cl2:0.1Eu2+ sample are obtained and assigned. The major one (2.71eV≈456nm) should be the emission of Eu2+ at 6h site. The minor one (2.61eV≈465nm) should be that of Eu2+ at 4f site.