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 ~ { } 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 { H _ { 2 } } abundance , and show that the cases with low metallicities ( \lesssim 10 ^ { -2 } ~ { } Z _ { \odot } ) or high { H _ { 2 } } abundance ( \gtrsim 10 ^ { -3 } ) can not form massive cold clouds with \gtrsim 10 ^ { 3 } ~ { } { M _ { \odot } } .