By adjusting the proportion of the host composition,the crystal structure,the luminescent properties and the long afterglow characteristics of phosphor SrAl2xO3x+1:Eu2+,Dy3+(x=1-2) are studied. Selecting strontium nitrate and aluminum nitrate as raw materials of host,ammonium borate and aluminum fluoride as fluxes,and using cationic oxalic acid co-precipitation,wet mixing,stepwise synthesis etc.,a series of long-afterglow phosphors with high brightness,long duration and good particle-size distribution are prepared. Based on the analyses on the X-ray diffraction (XRD) pattern,the scanning electron microscope (SEM) micrographs,the excitation and emission spectra and the afterglow decay curve of the sample,it is found that SrAl2xO3x+1:Eu2+,Dy3+ has a good crystal structure,the emission peak shows blueshift from 520 nm to 470 nm and the afterglow time for attenuation to recognizable luminous intensity (0.32 mcd/m2) is extended from 30 h to above 60 h when x increases. The study found that the main reason of different afterglow is that there are two types of Eu2+ luminous centers (blue and green-emitting) with different concentration and different fluorescence-decay time in the host. The fluorescence lifetime of blue-emitting center is apparently longer than that of the green emitting center.