The present invention relates to a fluorine-containing magnesium oxide powder using a vapor phase reaction and a method of preparing the same and more particularly to a fluorine-containing magnesium oxide powder brings about a cathode-luminescence emission having a peak within a wavelength range of 220 to 320 nm upon being excited by electron beams. The present invention provides a fluorine-containing magnesium oxide powder using a vapor phase reaction that sprays fluorine-containing gas and oxygen-containing gas to magnesium vapor, and the purity of magnesium oxide containing fluorine (i.e. the purity of fluorine-containing magnesium oxide) of 0.001 to 2 wt % is at least 98 wt % and a BET specific surface area thereof is 0.1 to 50 m2/g.