Abstract: A one-dimensional mathematical model based on heat transfer and reaction kinetics was developed for an oxygen blast furnace and was validated with the operating conditions and dissected data of a conventional blast furnace. The influence of oxygen concentration and upper gas volume on the smooth operation and process variables of the oxygen blast furnace was investigated by the model combined with coal combustion at tuyeres and top gas balance for separation and preheating. When the oxygen blast furnace with top gas recycling is of low oxygen concentration and upper gas volume, the reduction of iron ore is worsen and massive unreduced iron oxide comes into slag. In the oxygen blast furnace with top gas recycling, oxygen concentration and upper gas volume have significant effect on the temperature, reducing ability of gas and reduction rate. A comparative analysis of the conventional blast furnace and the oxygen blast furnace with top gas recycling show that the oxygen blast furnace has a higher reducing ability of gas (1.0 to 1.5 times higher for CO content), faster reduction rate (1.49 m higher for the position of ore reduction), and less direct reduction (55.2% to 79.2% less for direct reduction degree).