Oxygen strongly degrades the properties of AlN crystals, thus reducing oxygen concentration in AlN single crystals is a hot topic in the research of AlN crystal growth. Prior to AlN crystal growth, hightemperature sintering process is commonly employed to reduce oxygen concentration in AlN powder source. In this paper, the oxygen deposition behavior on crucible lids under different sintering conditions was investigated by the XRD analysis and EGA measurement. The results show that holding at 900~1100℃ under vacuum together with holding at 1500℃ under highpurity nitrogen atmosphere for several hours can greatly promote the oxygen deposition on the crucible lid at the early sintering stage. Further increasing the holding temperature to 2000~2100℃ under highpurity nitrogen atmosphere, the oxygen deposited on the crucible lid decreases dramatically, and a brown colored AlN crystallized layer with very low oxygen concentration will form on the deposition surface, which implies that oxygen impurity in AlN powder source was removed remarkably by combined sintering process.