The beta-stabilizing effects of the 3d transition metals in Ti were investigated by the first principles method. Especially, the beta-stabilizing effects of the group VIIB and group VIII metals Mn, Fe, Co and Ni in Ti were explored. The calculated results showed that Mn, Fe and Co have stronger beta-stabilizing effects than Cr and Ni in Ti, though all have the same Pauling valences. This result can be understood by the chemical bonding analysis, when the atom-size factor is proven to account little. Based on the calculated results, the valences of Mn, Fe and Co were suggested to be 6.5, 6.6 and 6.4 in the design of beta-type Ti alloy, instead of the frequently-used Pauling valence.