The composite powder of Al(OH)3 and Sr(OH)2, was obtained by means of the hydrolysis of the activated Al-Sr alloy powder in pure water. As a precursor, it could be used to prepare long after phosphor Eu, Dy co-doped SrAl2O4 by the modified solid state reaction at 1300°C. The components and microstructure of the composite powder were investigated by XRD, SEM and EDS techniques, and the luminescent characteristics and the afterglow properties of the long afterglow material were also measured at the same time. The experimental results showed that, the distribution of the two elements Al and Sr was uniform in the microstructure of the composite powder, and the contacting surfaces between the solid reactants were increased effectively at high temperature, and the diffusive paths were abbreviated. Therefore, the reaction velocity was increased, the sinter temperature descended and the luminescent properties enhanced.