Local-structures of a thermotropic cubic phase forming molecule, 1,2-bis-[4-n-octyloxy benzoyl]-hydrazine (BABH8) were studied by molecular dynamics simulations. Spontaneous formation of hydrogen bond networks and smectic ordered clusters were obtained in these simulations. Furthermore, spontaneous segregation was observed in the simulations with the artificial binary system which was composed separately of BABH8 mesogen cores and alkyl tails. These results indicate that the BABH8 core and tails have a strong tendency to segregate and the smectic order formation is promoted by intermolecular hydrogen-bonding of the core hydrazine group. Connections between this segregation character and cubic phase formation were discussed.