The　microstructure　of　the　room　temperature　ferromagnetic　semiconductor　Zn1-xCox-O1-δ　was　investigated　by　analytical　electron　microscopy.　The　experimental　results　indicated　that　the　oxygen　content　decided　the　microstructure　and　the　magnetic　property　of　Zn1-xCoxO1-δ.　The　films　deposited　under　poor　oxygen　consist　of　5　nm　sized　wurtzite　Zn1-xCoxO1-δ　and　amorphous　Zn-Co-O　between　them,　of　which　both　are　ferromagnetic　phases.　The　films　deposited　under　rich　oxygen　consist　of　10-20　nm　Zn1-xCoxO1-δ　and　antiferromagnetic　phase　CoO,　the　concentration　of　the　oxygen　vacancy　in　wurtzite　is　greatly　reduced,　and　the　room　temperature　ferromagnetism　is　greatly　weakened　and　even　disappeared.