The　Al2O3　powders　doped　with　different　mole　fractions　of　Er3+　and　those　co-doped　with　Er3+　ion　of　0.5%　and　different　mole　fractions　of　Y3+　ion　were　prepared　by　a　sol-gel　method.　Due　to　the　radius　difference　between　Y3+　ion　and　Al3+　ion,　the　microstructure　of　Al2O3　could　be　modulated　by　co-doping　with　different　mole　fractions　of　Y3+.　The　structure　of　the　powder　samples　were　determined　by　X-ray　diffraction　and　transmission　electron　microscopy,　respectively,　and　the　photoluminescence　(PL)　characteristics　were　analyzed　via　the　PL　spectra.　The　results　show　that　the　primary　phase　of　Y3+　and　Er3+　co-doped　Al2O3　samples　is　δ-Al2O3.　The　lattice　defects,　the　PL　intensity,　spectral　width　and　PL　lifetime　of　samples　increased　with　increasing　the　doping　quantity　of　Y3+　ion.　The　PL　property　of　Er3+-doped　Al2O3　powders　was　improved　effectively　via　the　modulation　of　the　microstructure　environment　of　Er3+　by　doping　with　different　quantities　of　Y3+　ion.