The volatilization of heavy metals in oil sludge (OS) restricts the development of OS incineration. In order to explore the effect of CaO on the migration characteristics of heavy metals during OS incineration, incineration experiments of OS with and without CaO were carried out respectively in a horizontal tube furnace at the temperature ranging from 800 degrees C to 1000 degrees C. The total amount, speciation fractions, and leachability of Cr, Cu and Zn in OS and bottom ash were investigated and presented in this work. The results showed that the total amount of Cr, Cu, and Zn in the bottom ash decreased with the increasing of experimental temperature. CaO could solidify the heavy metals in the bottom ash with an order of Cu, Cr, and Zn from strong to weak. In the presence of CaO additive, the exchangeable and acid-soluble fractions of Cu and Zn in bottom ash were significantly reduced. Moreover, the leaching levels of Cr, Cu and Zn in bottom ash were also obviously lowered. The results will supply essential data and theoretical support for the innocuous treatment of heavy metals in the bottom ash of OS incineration. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.