Metallurgical defects and the changes of O，N and S contents in superalloy IN792 were studied in the different refining processes. S content was measured using CS analysis apparatus, O and N contents were measured by TC-436 measurement apparatus, the mechanical properties of alloy were measured, also. The results show that shrinkage is easier to produce with increasing of O and N contents, and the contents of impurities are increased with increment of the contents of O，N and S. When the refining temperature is higher and refining time is longer, the contents of O，N and S are decreased, the UTS and YS are improved at room temperature.