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