Based on the theory of flows through porous media and coupled heat and moisture transfer, the momentum equation, energy equation and water conservation equation for interior of grain pile in squat silo were derived. The problems such as natural convection, heat transfer and moisture transfer of stored grain were solved by numerical solution. The ventilation effect of cross ventilation duct, annular ventilation duct and combined (cross and annular type) ventilation duct of squat silo was analyzed by numerical simulation with Fortran language. The results show that air distribution in combined (cross and annular type) ventilation duct are more evenly than that in the other two types of air ducts, which has the best effect of cooling and water conservation, therefore more propitious to the safe storage and energy saving. The result can provide theoretical guidance and basis for the selection and design of ventilation duct for squat silos.