Abstract: Aluminum nitride ceramics have become the important packaging materials for integrated circuits, semiconductors, and high-power devices due to the excellent thermal conductivity. The oxygen impurities in aluminum nitride ceramics directly affect the thermal conductivity. Thus, it is important to accurately determine the oxygen content (mass fraction) and distribution in aluminum nitride ceramics. Based on the inert melting infrared absorption method, the analysis methods of oxygen mass fraction in different forms in the aluminum nitride ceramics were studied. The mass fraction of surface adsorption oxygen, grain boundary oxygen, and lattice oxygen in the nitride ceramics was measured separately by the stepped heating method. The influence of crucible and auxiliary material selection on the measurement process and test results was discussed. The effect of graphite powder content on the release of grain boundary oxygen was analyzed. Finally, the heating program, the order of adding powder, and weight were optimized. The measurement method accuracy was verified by the multiple parallel tests on the aluminum nitride ceramics. In the results, the relative standard deviations of the measured grain boundary oxygen and lattice oxygen content are 4.5% and 8.5%, respectively, meeting the requirements of the relevant scientific research.