Abstract: In order to study the influence mechanism of micro pore geometry of sedimentary rock on its water absorption characteristics, based on Hagen-Poiseuille equation, Laplace-Young equation and fractal geometry theory, the capillary water absorption models which is respectively represented by average and fractal geometry are established by taking into account three geometric characteristics of pore section shape, pore size distribution and tortuous pore space.Compared with the existing model, the applicability and validity of representative model are verified by using existing experimental data.Finally, the sensitivity of geometric parameters influencing water absorption characteristics of pore structure is analyzed in detail.The results show that the parameters of water absorption characteristics are related to the pore geometry shape, tortuous fluid channel, free porosity and maximum pore size, whereas the more irregular the pore geometry and the more tortuous the connected pore channel, the stronger the heterogeneity and anisotropy of pore structure, and the weaker the water absorption.The physical meaning of equivalent average pore diameter is not clear in the model represented by average geometry, and the calculation result is larger than the measured values when average space pore size is directly brought into the model, while the physical meaning of parameters is clear in the model represented by fractal geometry, and the results close to measured values can be obtained; the proposed models have strong applicability for the pore structure with weak 3D pore connectivity and pore roar characteristics, and compared with the complicated IFU model and BEA model, similar or even more accurate theoretical predicted results can be obtained based on the simplified models.