We present a first principle study of Cr-doped In2O3 system using density func- tional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and converges to high spin-polarized configuration in the ground state. The hybridization between d-states and the donor states is strong, and the spin-split donor impurity-band model is found to be the most favorable mechanism for the ferromagnetism in this system. The good ferromagnetic property of high Curie temperature is discussed in view of the electronic structure analyses.