The structural, half-metallic (HM) and magnetic properties of the imperfect Pb₂FeReO₆ containing eight different inherent defects of the Fe_Re or Re_Fe antisites, Fe1-Re1 or Fe1-Re4 interchanges, V_Fe, V_Re, V_O or V_Pb vacancies have been studied by first-principles calculations. No obvious structural changes are observed for Fe_Re or Re_Fe antisites, Fe1-Re1 or Fe1-Re4 interchanges and V_Pb vacancy defects, however, the six (two) nearest neighbors O (Fe or Re) of the vacancy move away from (close to) V_Fe or V_Re (V_O) vacancies. The HM character is maintained for Fe_Re or Re_Fe antisites, far Fe1-Re4 interchange, V_Fe, V_O or V_Pb vacancies, while vanished for near Fe1-Re1 interchange or V_Re vacancy. So the near Fe1-Re1 interchange or V_Re vacancy defects should be avoided to preserve the HM character of the Pb₂FeReO₆ and thus usable in spintronics devices. Except for the Fe_Re antisite case with a slightly higher total moment, the total moments tot of the imperfect Pb₂FeReO₆ with the other seven inherent defects are smaller than 3.96 B/f.u. of the perfect Pb₂FeReO₆.