A mathematical time-dependent and isothermal model based on the grain model has been developed to simulate the kinetic and thermal behaviors of a porous iron oxide pellet undergoing chemical reactions with a mixture of hydrogen. carbon monoxide. carbon dioxide and water vapor. Its novelty consists in fact that it can deal with a multi-species reducing gas and oxide pellet. In spite of previous models in which the pure reductant was applied as reducing gas. this model can indicate an actual view of pellet reduction including the effects of reducing gas utility and reducing gas ratio. A finite volume fully implicit technique was applied for solving the governing equations. The model has been validated by comparing with experimental results from the literature. Finally. the effects of reducing gas parameters including gas ratio, gas utility. temperature. and pellet characteristics such as diameter, porosity and tortuosity factor oil the rate of reduction have been investigated.