The　plasma　brightness　cannot　be　used　as　a　direct　indicator　of　ablation　depth　detection　by　femtosecond　laser　was　experimentally　demonstrated,　which　led　to　the　difficulty　of　depth　measurement　in　the　maching　process.　The　tests　of　microchannel　milling　on　the　silicon　wafer　were　carried　out　in　the　micromachining　center　in　order　to　obtain　the　influences　of　parameters　on　the　ablation　depth.　The　test　results　showed　that　the　defocusing　distance　had　no　significant　impact　on　ablation　depth　in　LAV　effective　range.　Meanwhile,　the　reason　of　this　was　explained　in　this　paper　based　on　the　theoretical　analysis　and　simulation　calculation.　Then　it　was　proven　that　the　ablation　depth　mainly　depends　on　laser　fluence,　step　distance　and　scanning　velocity.　Finally,　a　research　was　further　carried　out　to　study　the　laser　parameters　which　relate　with　the　microchannel　ablation　depth　inside　the　quartz　glass　for　more　efficiency　and　less　cost　in　processing　by　femtosecond　laser.　©　2017　Elsevier　Ltd