  Star formation in high-redshift dwarf galaxies is a key to understand early
galaxy evolution in the early Universe. Using the three-dimensional
hydrodynamics code GIZMO, we study the formation mechanism of cold,
high-density gas clouds in interacting dwarf galaxies with halo masses of $\sim
3 \times 10^{7}~M_{\odot}$, which are likely to be the formation sites of early
star clusters. Our simulations can resolve both the structure of interstellar
medium on small scales of $\lesssim 0.1$ pc and the galactic disk
simultaneously. We find that the cold gas clouds form in the post-shock region
via thermal instability due to metal-line cooling, when the cooling time is
shorter than the galactic dynamical time. The mass function of cold clouds
shows almost a power-law initially with an upper limit of thermally unstable
scale. We find that some clouds merge into more massive ones with $\gtrsim
10^{4}~M_{\odot}$ within $\sim 2~{\rm Myr}$. Only the massive cold clouds with
$\gtrsim 10^{3}~M_{\odot}$ can keep collapsing due to gravitational
instability, resulting in the formation of star clusters. In addition, we
investigate the dependence of cloud mass function on metallicity and ${\rm
H_{2}}$ abundance, and show that the cases with low metallicities ($\lesssim
10^{-2}~Z_{\odot}$) or high ${\rm H_{2}}$ abundance ($\gtrsim 10^{-3}$) cannot
form massive cold clouds with $\gtrsim 10^{3}~M_{\odot}$.
