Our newly developed our original multi-scale simulator was applied to dye-sensitized solar cells (DSSC) to investigate the effect of the complex porous structure of a TiO2 electrode on cell performance. We simulated the current-voltage (/-V) characteristics for various models of porous structures of DSSCs including c/s-di(thiocyanato)-bis(2,2'-bipyridyl-4,4'- dicarboxylic acid)-ruthenium(II) (N3 dye). The short-circuit current density increased with decreasing porosity, overlap ratio, and particle diameter. A DSSC system including TA-St-CA (C30H22N2O 2) as a sensitizer was also investigated for comparison with the system with N3 dye. The dependence of the amount of dye adsorption on the /-V characteristics was evaluated. A linear relation between the short-circuit current density and the amount of dye adsorption was found. The obtained results indicate that our developed multi-scale simulator is a powerful tool for obtaining insights into the effect of properties in DSSCs and for optimizing the DSSC structure.