The present invention discloses a nitroxide fluorescent powder comprising an inorganic compound containing M, A, B, O, N, and R elements; in which the M element is at least one of Ca, Sr, Ba, Mg, Li, Na, and K, the A element is at least one of B, Al, Ga, and In, the B element is at least one of C, Si, Ge, and Sn, the R element is at least one of Ce, Eu, Lu, Dy, Gd, and Ho, characterized in that the inorganic compound forms a crystal in a crystalline phase, and the oxygen atom content in the crystal in a crystalline phase is in an increasing structural distribution from a core to surface of the crystal. The nitroxide fluorescent powder and the nitroxide illuminant of the present invention have the advantages of good chemical stability, good aging and light decay resistance, and high luminescent efficiency, and are useful for various luminescent devices. The preparation method of the present invention is easy and reliable and useful for industrial mass production.