A deep understanding of ion desolvation in microporous electrodes is helpful for achieving efficient energy storage. Herein, we evaluate the contribution of ion desolvation to electrochemical performance of microporous electrodes with a proposed multiscale approach. By integrating the molecular version with the simple version of classical density functional theory, we first determine the solvation diameters of ions in confined molecular solvent, and then predict the capacitances of microporous electrodes through a solvation-diameter-dependent coarse-grained model. We find that the solvation diameter displays an oscillatory decline as decreasing the pore size of nanoslit, and upon this relation in combination with the pore size distribution of microporous electrode we give satisfactory predictions of the capacitances of practical electrodes compared with experimental measurements. This work not only provides a feasible multiscale tool for predicting the capacitances of microporous electrodes involving liquid electrolytes, but also casts insights for the design and preparation of high-performance supercapacitors.