During the stainless steel smelting process, the control of the slag skimming process affects the formation of hexavalent chromium in the stainless-steel slag. However, the hazardous problem of hexavalent chromium in stainless-steel slag has been a major factor limiting its resource utilization. In this paper, by studying the enrichment form of chromium in stainless-steel slag and the formation mechanism of hexavalent chromium, the cooling system and the content of additives were controlled in the slag skimming process to reduce the formation of hexavalent chromium. Different means of characterization including TG-DSC, phase diagram, FT-IR, XPS, potential-pH equilibrium diagram and HJ 687-2014 method were used to characterize the presence and content change of hexavalent chromium in solid and leachate. Results showed that hexavalent chromium formation mechanism was related with the chromium diffusion in two typical Cr-containing components in stainless-steel slag. A slow cooling rate can reduce the emission of Cr(VI) in stainless-steel slag. A lower addition of boron oxide content made a lower emission of hexavalent chromium. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.