The　relationships　between　focal　position　and　diameter　or　taper　of　holes　drilled　by　CO2　laser　in　ceramics　were　investigated　by　a　new　method　named　＇equivalent　stack　plate　method＇(ESPM).The　diameter　of　holes　in　different　depth　can　be　accurately　measured　by　the　new　method.　The　present　study　reported　a　statistical　analysis　to　study　the　effects　of　the　focal　position　on　the　quality　of　the　drilled　holes　and　optimization　of　the　processing　parameter.　The　study　was　conducted　based　on　the　statistical　experiments　with　the　variable　focal　position　from　+1mm　to　-3mm.　Then　the　relationship　between　focal　position　and　diameter　in　different　depth　and　corresponding　mathematical　model　were　ascertained　by　polynomial　fitting　analysis.　The　unique　characteristics　of　ceramic　during　laser　drilling　were　also　discussed.　The　results　indicate　that　the　ideal　focal　position　to　achieve　minimum　taper　in　laser　drilling　holes　should　be　set　above　the　surface　of　workpiece.