The influence of upper shaft profile and burden properties on gas velocity distribution and formation of mixed zone near wall was analyzed by using both a sector and a half section three-dimensional cold models of blast furnace. In the case of upper shaft profile with damage, the mixed zone near wall is formed, the gas velocity near wall increases 1.52.5 times and the high gas velocity region expands 1.52.0 times as compared with these in the case of normal upper shaft profile. This phenomenon is developed as the small ore ratio in the burden increases. The mixed zone near wall in upper shaft is formed by delaying of coke descent and percolation of small ore due to the drastic change of cross section area or the increase of friction angle between wall and burden. At Kimitsu No. 2 BF, the deviation of CO gas utilization ηco near wall decreased and the average of CO gas utilization ηco increased after the repair of upper shaft profile.
