  Using 3D hydrodynamic calculations we simulate formation of molecular clouds
in the Galaxy. The simulations take into account molecular hydrogen chemical
kinetics, cooling and heating processes. Comprehensive gravitational potential
accounts for contributions from the stellar bulge, two and four armed spiral
structure, stellar disk, dark halo and takes into account self-gravitation of
the gaseous component. Gas clouds in our model form in the spiral arms due to
shear and wiggle instabilities and turn into molecular clouds after $t\simgt
100$ Myr. At the times $t\sim 100 - 300$ Myr the clouds form hierarchical
structures and agglomerations with the sizes of 100 pc and greater. We analyze
physical properties of the simulated clouds and find that synthetic statistical
distributions like mass spectrum, "mass-size" relation and velocity dispersion
are close to those observed in the Galaxy. The synthetic $l-v$ (galactic
longitude - radial velocity) diagram of the simulated molecular gas
distribution resembles observed one and displays a structure with appearance
similar to Molecular Ring of the Galaxy. Existence of this structure in our
modelling can be explained by superposition of emission from the galactic bar
and the spiral arms at $\sim$3-4 kpc.
