Abstract: Through the different pyrolysis time tests in 200 kg coke oven of lump coal mainly used in melter gasifier, namely A coal and B coal, the size distribution and strength change of the two coals after coking was compared. Results showed that the pulverization of B coal in coke oven was severe, which size degradation rate (DR) was always increasing with the coking time prolonging. On the contrary, the DR of A coal was decreasing once reached the maximum value. The mineral microstructure of semi coke formed by the two coal pyrolysis in coke oven was also compared. It was found that semi coke formed by A coal was mainly mosaic and isotropy stucture, and the other semi coke formed by B coal was mainly fusain and isotropy structure. There was still some coal residue in both semi cokes. Through the mineral microstructure analysis of different particle size of carbon-containing materials in tuyere samples taken out from melter gasifier, it was found that the particles less than 6.3 mm in hearth were caused by the semi coke pulverization. Moreover, the pulverization of semi coke was mainly form B coal.