In most of numerical simulations of spiral galaxy formation,mass/spatial resolution is ~ 105-6 M๏ and kpc or sub-kpc,therefore inhomogeneous structure of the ISM in galaxies is notresolved. This is the most serious defect in simulating starformation and its feedback during galaxy formation/evolution. Here weshow an intrinsic structures of the ISM using 3-D high resolutionhydrodynamic simulations of galactic disks. We show that the PDFs inglobally stable, inhomogeneous ISM in galactic disks are well fittedby a single log-normal function over a wide density range. Thedispersion of the log-normal PDF (LN-PDF) is larger for more gas-richsystems. Using the LN-PDF, we give a generalized version ofSchmidt-Kennicutt law, i.e. SFR as a function of average gas density,a critical local density for star formation, and star formationefficiency. We also introduce our new project, “Project Milky Way”, in which weaim to resolve properly the cold, dense ISM, as found in abovesimulations, by ultra-high resolution during galaxy formation. We areplanning to construct a special cluster for simulating formation of“Milky Way” using the next generation GRAPE.