Sulfur is the main element which caused Nickel-based alloy embrittlement. In this study, the sulfur in Hastelloy X superalloy was determinated with Auger Electron Spectroscopy (AES) for samples quenched from 1180 °C and aged at 500 °C for different time. Experiments results confirmed the non-equilibrium segregation characteristics of sulfur. The results showed that a segregation peak of sulfur is at about 20 min during ageing. This peak was satisfactorily elucidated by the theory of non-equilibrium grain-boundary segregation. By theoretical calculation, the critical time constant of impurities sulfur atom in the Hastelloy X δs= 357. At the same time, the result provides a theoretical basis for sulfur segregation mechanism.