Abstract: An oxygen blast furnace was divided into the three zones of hot zone, solid charging zone and gas heating zone. Physical constraints and chemical constraints of each zone were analyzed in detail. Based on material balances and energy balances, a multizone constrained mathematical model was established for oxygen blast furnaces. Theoretical analysis and calculation results show that the multi-zone constrained mathematical model can make up for deficiencies in the whole furnace heat balance and reflect the heat value in use of different zones. The solid charging zone is constrained by indirect reduction and heat balances. With the increase of metallization rate, the need of cycle gas is increased in the solid charging zone. When the metallization rate is very high, the hot zone and solid charging zone meet the thermal equilibrium conditions; although the calculated fuel ratio is low, the gas volume in the gas heating zone can not achieve balance.