Thermal　conductivity　of　MOX　fuel　is　one　of　the　key　parameters　to　influence　its　service　performance　in　reactor.　However,　the　thermal　conductivity　variation　of　MOX　fuels　with　composition　is　usually　determined　by　the　empirical　formula　obtained　from　the　experimental　data,　and　few　investigations　have　been　conducted　on　a　theoretical　basis.　In　this　study,　the　effect　of　various　point　defects　on　the　thermal　conductivity　of　MOX　fuel　was　investigated　by　analyzing　the　influence　factors　of　thermal　conductivity　for　MOX　samples　with　different　Pu　content　and　0/M　in　light　of　the　classical　phonon　conduction　theory.　The　results　show　that　the　phonon　conduction　models　can　be　used　to　predict　the　thermal　conductivity　of　MOX　fuels　with　different　compositions.　The　oxygen　vacancies　induced　by　hypo-stoichiometry　in　MOX　fuel　predominate　in　determining　the　thermal　conductivity,　rather　than　the　substituted　ions　point　defects　with　small　mass　and　radius　difference.