The　processing　of　an　ultra-short　pulse　laser　is　widely　discussed　and　used　in　the　field　of　micro　machining,　especially　for　precision　processing　of　the　hard　and　brittle　materials.　Firstly,　the　ablation　ability　would　reduce　with　the　defocusing　distance　increase　in　theory.　However,　it　was　found　that　the　microchannel　ablation　depth　is　not　sensitive　to　the　defocusing　distance　in　the　experiments.　The　theoretical　analysis　and　simulation　calculation　were　carried　out　in　this　paper　in　order　to　explain　the　reason　for　the　relationship　between　them.　Secondly,　the　size　of　microchannel　structure　of　the　silicon　wafer　and　quartz　glass　in　our　experiments　were　determined　obviously　by　the　main　processing　parameters　of　femtosecond　laser.　Furthermore,　the　influence　of　laser　parameters　on　the　structure　size　was　studied.　It　was　proven　that　the　high　quality　processed　of　microchannel　depend　on　the　reasonable　selection　and　combination　of　the　parameters　by　femtosecond　laser,　which　provided　an　important　suggestion　to　process　microchannel　precisely.　©　2018　Elsevier　Ltd