Oil sludge (OS) is a typical hazardous waste from the petrochemical industry. Currently, the increasing ratio of highsulfur crude oil worldwide that results in the growth production of OS with high sulfur content has drawn much attention. OS incineration with calcium-based additives has great potential to be an efficient and clean approach for the large-scale treatment of high-sulfur-containing OS. In this work, the migration characteristics of sulfur and nitrogen during OS combustion with CaO additives were investigated by an online thermogravimetric-mass spectroscopy-Fourier transform infrared (TG-MS-FTIR) spectroscopy system and a fluidized combustion reactor system, respectively. Results indicated that CaO significantly reduced the emissions of SO 2 and NO x during fluidized combustion of OS, and the minerals in OS and CO 2 in the flue gas affected the utilization efficiency of CaO additive. The sulfur fixation capacity by CaO decreased with the increase of combustion temperature and almost completely failed at 1100 °C. The capacity of CaO to reduce NO x emission increased first followed by a decrease with the increase of combustion temperature. Furthermore, CaO significantly promoted the conversion of HCN to other nitrogen-containing gases, which can promote the production of NO by the precursors (HCN and NH 3 ) and the reduction reaction of NO to N 2 . To the best of our knowledge, there is still not an efficient and clean technology for large-scale treatment of OS in China. This study is helpful for the massive utilization of high-sulfur-containing OS.