Abstract: Coal gasification slag is a kind of solid waste produced from coal gasification process. In this paper,five kinds of gasification slag were selected. The chemical structure and microstructure of the slags were studied firstly. Then,the phase composition and microstructure of nitridation products obtained by carbothermal reduction nitridation (CRN) of slags at 1 350-1 500 ℃ were comprehensively investigated. The results show that:① The chemical struc- ture of five kinds of amorphous slag can be generally described as the frame structure of SiO4 tetrahedra branched with AlO4 tetrahedra;② The glass phase in slag tends to exist in spherical shape,whereas the amorphous carbon tends to stay in porous sponge,long strip or sheet-like shape;③ Ca-α-SiAlON can be synthesized from CRN of each slag. Mo- reover,the formation steps of Ca-α-SiAlON in each CRN process are the same;④ The formation of impurity in nitrida- tion products is closely related to the relative content of CaO,SiO2 ,Al2 O3 and C in raw slag;⑤ During the CRN process,the morphological evolution of glass balls in raw slag can be used as the indicator showing the process of CRN,such as rough surface,porous or hollow structure.