Characteristics of the gas-solid reduction reaction between iron ore sinter and CO gas at 1 273 K were studied with Thermal-Gravity analyzer.The samples used in current study are industrial iron ore sinter produced in Shougang sintering plant.The Thermal-Gravity analyzer was produced in CAHN Corporation from German,the balance accuracy and max temperature of which was 1.0 pdg and 1 735C respectively.The study mainly focused on the mineral composition,microstructure changes and porosity changes during various stages of the reduction.The micro-structure,mineral compositions and porosity of sample before reduction,300-/o reduced sample,700-/o reduced sample and fully reduced sample were investigated.It was found that the reduction rate decreased with higher reduction degree due to the mineral composition changes during the reduction.The hematite and calcium ferrite in the sinter was firstly reduced during the reduction due to its good reducibility.The reduction rate of hematite is higher than that of calcium ferrite.At the reduction degree of 300-/o,the original mineral phases and structures remained in the core area of the sample.The reduction reaction of hematite-ymagnetite and calcium ferritemagnetite occurred in the outer layer.The hematite and calcium ferrite was reduced t0 44.4% and 60.40-/. respectively.At the reduction degree of 700-/o,all the hematite,calcium ferrite and magnetite in the outer layer were reduced to metal iron,only 360-/o wustite was left in the core area.Some original structures such as columnar structure and mixed structure can be observed in some area of 700-/o reduced sample.Most of the area in the reduced sample appeared to be even metal iron layer due to the nucleation and growth of the metal iron;lt can be found that loose structures and cracks were generated during the reduction from calcium ferrite to magnetite.The reduction reaction began with the loose structures and spread to the nearby area.In the area of micro-pores,the reducing gas can easily diffuse to the reaction interface to proceed the reduction reaction effectively.So increasing the content of micro-pores is an effective way to improve the reducibility of the sinter.According to the porosity testing results,the porosity of the sample increased from 12.43 0-10 t0 53.440-/o after reduction,and most of the increment happened in the early stage of the reduction.