The structural stability, electronic, magnetic and optical properties of the Fe doped CoS2 bulk alloy and the thin films with different terminations are studied by the first-principle calculations. The bulk Co0.75Fe0.25S2 alloy is 100% spin polarized, and there are new impurity valence bands near Fermi level in both the spin-up and spin-down channels of the band structures. The fracture of Co-S or Fe-S chemical bonds and the change of S-S dimer bonds are the key factors affecting the properties of the films. The surface energy of SS-SS-CoCo termination film under the S-rich and Co-rich boundary conditions is the lowest, and spin polarization maintains -100%. Although the spin polarization of CoFe terminated film is high (-90.2%), but its surface energy is high which lead to the unstable feature. The magnetic moment of the thin film is mainly contributed by the spin magnetic moment of the Co and Fe atoms. The magnetic moments of the atoms at outer layer differ significantly from those at the central layer due to the change of crystal field and the influence of surface effect. Fe doping and termination selection can modulate the optical properties of CoS2 effectively.

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