The　content　of　this　paper　is　a　design　of　zoom　optic　system　applied　in　248nm　KrF　excimer　laser　micro-processing.　Due　to　the　characteristic　of　KrF　laser　and　the　applied　requests　of　micro-processing,　it　was　determined　that　the　maximal　field　of　view　is　1.2°,　the　optical　material　is　fused　quartz　(JGS1)　and　the　value　of　working　distance　is　greater　than　30mm.　On　the　premise　that　the　system　has　stable　image　surfaces　and　good　imaging　qualities　under　each　different　focal　length,　the　goals　of　design　include　the　continuous　zoom　ratio　Γ=1　∼3.5　and　the　minimal　magnification　M0.1.　In　addition,　the　mechanically　compensated　method　was　employed　to　compensate　image　surface,　so　as　not　to　change　the　position　of　the　image　plane　in　the　whole　range　of　focal　lengths　or　magnification.　The　zoom　optical　system　was　composed　of　three　parts:　the　front　fixed　group,　the　zoom　group　and　the　compensated　group.　After　perfect　optical　calculation,　the　correlation　of　zoom　ratio　and　focal　length　was　obtained.　The　maximum　of　focal　length　is　129.2308mm　and　minimum　is　39.92926mm　when　M=0.1.　For　continuous　improvement　of　imaging　quality,　the　initial　configuration　has　been　optimized　by　making　use　of　ZEMAX®.　The　result　of　design　can　achieve　the　goal　of　zoom　ratio.　During　the　zoom　process,　the　total　length　of　system　is　about　290.7065mm　with　the　deviation　Δ=±0.0403mm　and　the　minimum　of　working　distance　is　59.3094mm.　The　whole　system　has　good　imaging　quality　and　effective　etching　capability.