Abstract: The gas-resistance characteristics of nitrogen foam produced in sand pack was studied at different gas injection pressure. The stability evaluation of foam in beaker and porous medium indicated that the initial residual resistance factor of foam to gas increased in power exponent with the increment of gas injection pressure. The residual resistance factor of foam to gas and water decreased in power exponent with equilibrium time. The stability of foam in beaker was greatly lower than that in the porous medium and increased linearly with the enhancement of environment pressure. The analysis on a simple pore model showed that good dispersion conditions and thicker membrane in the porous medium could be the main causes for above phenomena. The initial resistance factor of foam increased with the pore-throat ratio, and coalesce probability declined with the rising of throat length, which thus improved the stability of foam. The greater the heterogeneity of reservoir in pore scale network, the larger the gas pressure difference in pores. When the coalesce probability of gas enhancement gets bigger, the stability of foam will get worse.