The Eu2+ activated blue emitting BaAl2Si2O8：Eu2+ phosphor was synthesized by one-step calcination process of precursor prepared with chemical coprecipitation. X-ray diffraction （XRD），fluorescence spectrophotometry and scanning electron microscopy were used to investigate the structure，luminescent property and morphology of the BaAl2Si2O8：Eu2+ blue phosphor. The results showed that BaAl2Si2O8：Eu2+ phosphor synthesized by the process was pure. The crystal structure of BaAl2Si2O8 transformed from hexagonal structure to monoclinic structure after precursor doping H3BO3，which changed the emission peak and luminescence intensity of BaAl2Si2O8：Eu2+ phosphor. The luminescence intensity firstly increased with H3BO3 doping concentration increasing，then decreased. The optimum mass fraction of H3BO3 is about 1.5%. The use of H3BO3 as flux could help the phosphor to crystallize，thus enhance the intensities of the excitation and emission spectra of BaAl2Si2O8：Eu2+ phosphor，improve the morphology of particles，and endow them with round edges，smooth surfaces and nearly spherical shapes.