A series of Eu doped and charge compensated Sr5(PO4)3Cl phosphors have been synthesized via a solid-state reaction in air atmosphere. The XRD patterns and the Rietveld refinement confirmed that the obtained samples were pure phases. The photoluminescence properties of Sr5(PO4)3Cl:Eu phosphors exhibited that Eu3+ could be reduced to Eu2+ in an air atmosphere, and the corresponding mechanism of abnormal reduction of Eu3+ to Eu2+ had been discussed. Meanwhile, the enhancement in the PL intensity of red emission and the thermal stability of phosphors was observed upon co-doping via the charge balance strategies of (a) 2Sr2+ = Eu3+ + R+ (R = Li, Na and K), (b) Eu3+ + Si4+ = Sr2+ + P5+ and (c) 3Sr2+ = vacancy + 2Eu3+, among which Na+ ions had the optimized charge compensation effect. The mechanisms between different charge compensation methods and the improvement in PL intensities of Eu3+ were also analyzed.