Abstract: The environmental risks posed by hazardous heavy metal elements in coal gasification slag (CGS) present significant challenges to its safe disposal and green resource utilization. Understanding the occurrence characteristics and leaching behavior of these heavy metals elements is key to the harmless treatment of CGS. In this study, the sequential extraction method and three nationally issued toxicity leaching procedures were employed to investigate the occurrence forms and toxicity leaching characteristics of eight typical hazardous heavy metals in six CGS samples from related enterprises in Shaanxi and Ningxia.The results indicated that Cr, As, Mn, Ni, and Cu in CGS primarily existed in residual forms, while the weak acid extractable, reducible, and oxidizable forms of Zn, Pb, and Ba were more prevalent in fine slag. In contrast, the residual fractions of heavy metals were higher in coarse slag than in fine slag. Elements such as Ni, Pb and Zn in fine slag exhibited higher mobility and instability, while Ba showed greater mobility and instability in coarse slag.Environmental risk assessments of the six samples revealed that fine slag poses a higher potential risk than coarse slag. Under simulated normal rainfall conditions, the heavy metal content in all six CGS samples exceeded China’s groundwater Class Ⅲ standard limits. In the leaching experiments at disposal sites, only the leachate from the Pucheng coarse slag met the standard threshold requirements. Under simulated acid rain conditions, the leachate from fine slag exceeded the national hazardous waste landfill pollution control standards. However, the leachate from all six CGS samples remained within the toxicity identification limits, indicating that these CGS samples are classified as general solid waste. Nevertheless, they should not be disposed of by simple methods such as piling, landfilling, or sending to municipal waste treatment facilities.