Abstract: Occupancy,binding energy,state density,charge distribution and charge density difference of alloy atoms M(M = Mo,Nb,V) doped α-Fe(C) system were calculated by using the first principles method,and the solid-solution mechanism of alloy elements in α-Fe(C) was discussed from the atomic level. The results showed that Mo and Nb preferentially occupied the body center of the cell,whereas V preferentially occupied the apex angle of the cell. The binding energy of V was the highest,Mo was the second,and Nb was the lowest. Mo,Nb and V all formed metallic bond,covalent bond and weak ionic bond in the cell,and the orbitals whereby the bonding formed were mainly interactions of Mo4d with Fe3d,of Nb4d with Fe3d,of V3d with Fe3d and C2p.