Substitution is widely employed to design single-host phosphor with multiple sites for one activator, which could emit more than one band. BaSrMg(PO4)(2):Eu2+ was reported as a potential single-host white light-emitting phosphor for white LEDs, possessing multiple sites for Eu2+ doping. However, different emission spectra were observed in this paper for the sample with same nominal formula. Therefore, XRD and Rietveld refinements were employed to investigate the crystal structure in detail and the results indicated that the sample contains Sr2P2O7 coexisting with the main phase BaSrMg(PO4)(2). Meanwhile, BaSrMg(PO4)(2) phase was identified to be isostructural with Ba2Mg(PO4)(2) and was confirmed by TEM. Photoluminescence of the phosphor sintered at 900 degrees C shows two emission bands peaking at 424 and 585nm. Hence, different from the literature, the blue band was assigned to the 4f(6)5d(1)4f(7) transition of Eu2+ occupying the Sr2+ sites in Sr2P2O7 and the yellow band to the Eu2+ occupying Sr2+ and Ba2+ sites in BaSrMg(PO4)(2). The relative intensity ratio of yellow/blue bands is consistent with the content ratio of two phases in the samples with different synthesis temperatures, which is further proof for the original of the blue band. The results of the thermal quenching data demonstrated that the Sr2+-substituted phosphor was better than Ba2Mg(PO4)(2).