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Summary With a more complex pore system compared with clastic rocks, carbonate rocks have not yet been well described by the present conventional rock physics models concerning its vagary of pore geometry as well as the influence on elastic properties of rocks. To better understand the intrinsic effect on carbonate rocks’ properties, we propose a factor depicting the pore geometry of rocks based on conventional rock physics models in this paper. We start with a discussion and an analysis about the pore geometry of carbonate rocks. And then, we give introduction to a new approach of modeling carbonate rocks and construct a pore structure factor of carbonate rocks with a basis of the Gassmann equation and Eshelby-Walsh ellipsoid inclusion crack theory. Finally, we discuss the mutation relationship of pore structure factor with other elastic modulus parameters, analyze the pore structure factor with experiment data and logging data, and make a quantitative calculation of porosity. The results of theoretical study and case study reveal that the pore geometry of rocks can significantly influence the rocks’ elastic properties, and the approach we introduce can effectively decrease the predicted error of porosity and hence improves its prediction accuracy.