The Lurgi gasification technology has attracted significant commercial interest in China owing to its suitability for production of synthetic natural gas (SNG). However, hazardous trace elements (HTEs) in Lurgi gasification ash have the potential risk of contaminating surface and groundwater. In this paper, the HTEs in ash with different particle sizes from Lurgi gasifier and the HTEs concentrations of leachates were investigated by using an ICP-MS (Thermo Fisher, ELEMENT2/XR) and a direct mercury analyzer (DMA 80). Moreover, the mass loading (f(x)) and ecological risk index (RI) was introduced to evaluate the risk level of HTEs in Lurgi gasification ash with different particle sizes. The content of Be, Cr, Ni, Cu, Zn, Cd, Ba, Pb, U and As in fine ash (<3 mm) accounts for 40–55% of the total content. HTEs are more likely to concentrate in the fine ash with a particle size of less than 3 mm and a large specific surface area in the Lurgi gasifier. The pH range of the leachate is from 8.2 to 10.1. As and Cd presented the highest leachability, and more than 85.9% of As and over 54.1% of Cd in the ash were transferred into the leachate. The concentration of As, Cd, Be and Cr in the leachate is negatively correlated with the ash particle size, while Pb is positively correlated. The mass loading index of Lurgi ash with particle size of 3 ~ 6mm is the smallest, less than 10%. And the ecological risk index (RI) of Lurgi gasification ash increased with the decrease of particle size, but all of them were at low-risk level. However, in some cases, the leached concentrations of arsenic exceed the allowable limit of the secondary groundwater standard in China.