Abstract: The environmental risks posed by harmful heavy metals in coal gasification slag (CGS) present significant challenges for the safe disposal and sustainable use of CGS. Understanding the occurrence and leaching characteristics of these harmful heavy metals is crucial for effectively managing CGS. This study utilized a continuous extraction method and three characteristic toxic leaching methods issued by the state to investigate the occurrence forms and toxic leaching characteristics of eight typical harmful heavy metals in six types of CGS from enterprises in Shaanxi and Ningxia. The results indicate that in coal gasification slag (CGS), Cr, As, Mn, Ni, and Cu primarily exist in the residual fraction. Among these, the volatile elements Zn, Pb, and Ba in the fine slag primarily exist in higher proportions of acid-soluble, reducible and oxidizable fraction, while the residual state of metal elements in the coarse slag is higher than that in the fine slag. Elements such as Ni, Pb, and Zn in the fine slag show higher mobility and instability, whereas Ba in the coarse slag exhibits higher mobility and instability. Environmental risk assessment of the six samples reveals that the fine slag poses a higher potential risk than the coarse slag. Under simulated normal rainfall conditions, heavy metal elements in all six CGS samples exceed the Class III standard limit for groundwater in China. In leaching tests at the treatment plant, only the leachate of the coarse slag from Pucheng falls within the standard threshold. Under simulated acid rain conditions, the leachate of the fine slag from all six CGS samples exceeds the national standard for pollution control of hazardous waste landfill. However, the leachate of all six CGS samples does not exceed the leaching toxicity identification standard, indicating that these CGS samples belong to general solid waste. Nevertheless, CGS should not be treated in a simple and extensive manner such as landfilling, dumping, or incineration.