[en] The electronic and magnetic properties of the Co2FeGe full Heusler alloy in (001) thin film are investigated using the first-principles electronic structure calculations within the density functional theory. We employ various exchange correlation functionals including the local density approximation (LDA), the generalized gradient approximation (GGA), and the additional +U corrections for strong on-site Coulomb interaction of transition metal 3d states, aiming to examine the correlation effect on the electronic structures which determine the spin gap and thus the half-metallicity. Our results reveal that the Co2FeGe thin film is metallic in both LDA and GGA, while the +U correction opens up the spin gap for spin minority channel in GGA+U but not in LDA+U in contrast to its bulk alloy which is predicted to be half-metallic in both LDA+U and GGA+U approaches with total spin magnetic moment of 6 μB. It is found that the surface states developed around the Fermi level and the enhanced 3d eg-t2g band splitting for the spin minority channel due to the correlation effect play critical roles to determine the emergence of the half-metallicity.