In most of numerical simulations of spiral galaxy formation, mass/spatial resolution is ~ 105-6M๏ and kpc or sub-kpc, therefore inhomogeneous structure of the ISM in galaxies is not resolved. This is the most serious defect in simulating star formation and its feedback during galaxy formation/evolution. Here we show an intrinsic structures of the ISM using 3-D high resolution hydrodynamic simulations of galactic disks. We show that the PDFs in globally stable, inhomogeneous ISM in galactic disks are well fitted by a single log-normal function over a wide density range. The dispersion of the log-normal PDF (LN-PDF) is larger for more gas-rich systems. Using the LN-PDF, we give a generalized version of Schmidt-Kennicutt law, i.e. SFR as a function of average gas density, a critical local density for star formation, and star formation efficiency. We also introduce our new project, “Project Milky Way”, in which we aim to resolve properly the cold, dense ISM, as found in above simulations, by ultra-high resolution during galaxy formation. We are planning to construct a special cluster for simulating formation of “Milky Way” using the next generation GRAPE.