First-principles calculations are made on the Ge1-xMn xTe diluted magnetic semiconductors with different compositions. The origin of their ferromagnetism is investigated and the carrier-induced ferromagnetism is developed for these diluted magnetic semiconductors. The Mn 3dstates localized with divalent character are deep below the Fermi level, and the carriers introduced by defects are supported in our calculation. The pstates of Ge also play an important role in the occurrence of ferromagnetism especially at high temperature. It is thought that Ge1-xMn xTe with a moderate composition (x ≤ 0.51) of Mn atoms is a good candidate for DMS materials.