The absorption， electronic structure and luminescence spectrum of three Sillen bismuth oxyhalides， CaBiO2Cl， SrBiO2Cl and BaBiO2Cl， are reported and analyzed. The calculated electronic structure by the density functional theory shows that both SrBiO2Cl and BaBiO2Cl are semiconductors with direct band gap， which are consistent with the results of ultraviolet (UV)-vis diffuse reflectance experiment. The X-ray and UV excited luminescent spectra show a broad emission band extending from 400 to 550nm at room temperature. The light yield of BaBiO2Cl powders is about 1.4 times that of Bi4Ge3O12 (BGO) powders at room temperature under X-ray excitation， and BaBiO2Cl powders have shorter decay times of 100ns (22%)， 300ns (41%) and 600ns (37%)， compared with those of the BGO powders. The luminescence properties show a correlation between Bi—O(Cl) distance and radius of M2+ ions. Considering that the density of BaBiO2Cl is 6.98g/cm3， it may be a potential practical scintillator.