Abstract: The alloying effect on bulk moduli of TiH 2 systems is studied by performing the first principles calculation for a cluster model. It follows that the bulk moduli of alloyed TiH 2 firstly increases and then decreases with the atomic number of the alloying elements in the same period. ⅤB ⅧB group elements could keep or enhance the bulk moduli of TiH 2. This effect is stronger for 4d elements than 3d elements. The coincident dependence between the bulk moduli and metal Ti bonding with alloying element indicates that the bulk of hydride has obvious metallicity.