A local thermal stress model of water-cooled-wall pulverized-coal gasifier was built, and ANSYS was used to simulate the stress field in the gasifier operation to research the damage of refractories and slag layer caused by the thermal stress. The results reveal that: (1) the maximum stress of water-cooled-wall gasifier appears at the interface between anchor nails and refractories as well as the interface between refractories and the slag layer, and the maximum stress of slag layer appears on the surface of the slag layer; (2) the increase of slag layer thickness can significantly reduce the thermal stress at the interface between anchor nails and refractories, but increase the thermal stress between slag layer and refractories; (3) when the thermaI conductivity is 2-6 W · m-1 · K-1, the thermal stress increases rapidly with the increase of the thermal conductivity, but when the thermal conductivity is 6-10 W · m-1 · K-1, the thermal stress is basically stable; (4) the higher the cooling rate, the faster the decreasing speed of the temperature and thermal stress.