The melting/vitrification method is a promising approach for the large-scale, rapid, and harmless disposal of municipal solid waste incineration fly ash (MSWIFA). However, this method inevitably involves challenges related to secondary pollution. A 2 t/d pilot-scale melting furnace was built to investigate the distribution and migration of pollutant components-specifically heavy metals, sulfur, and chloride-within secondary fly ash (SFA), vitrified slag (VS), and ash in the flue gas channel (AFC) during the melting process of MSWIFA. The results demonstrate that the high-temperature melting process facilitated the migration of volatile heavy metals (Zn, Pb, Cu, and Cd) from MSWIFA to SFA. These metals exhibited strong leaching abilities, resulting in a high ecological risk index (RI) of 792, signifying an extremely high ecological risk and potential harm. Conversely, the high-temperature melting process promoted the migration of nonvolatile heavy metals (Cr, As, and Ni) from MSWIFA to VS, where their leaching was minimal, resulting in a low RI value of 47 and a correspondingly low potential ecological risk. Furthermore, the addition of auxiliary materials, quartz sand, and alumina facilitated the migration of volatile heavy metals from SFA to AFC while simultaneously promoting the migration of nonvolatile heavy metals from MSWIFA to VS. This redistribution effectively mitigated the harmful effects of SFA and enhanced the immobilization of heavy metals within the VS. Additionally, the migration characteristics of sulfur and chlorine pollutants were the same as those of volatile heavy metals. The addition of quartz sand and alumina effectively reduced the concentrations of SO