CO2　laser　direct-writing　ablation　micromachining　technique　is　used　to　fabricate　the　microchannel　on　the　polymethyl　methacrylate　(PMMA)　substrate.　The　correlation　between　the　process　parameters　(the　laser　power　and　the　beam　translational　velocity)　and　the　micromachining　quality　(the　depth　and　the　width　of　the　microchannel)　is　investigated.　A　laser　power　of　4.5　W　and　beam　translational　velocity　of　76.2　mm/s　is　used　to　make　ablation　of　the　microchannel　with　a　hydraulic　diameter　of　100　μm　on　the　PMMA　substrate.　The　time　for　the　ablation　process　is　30　s.　This　technique　is　steady　and　efficient　in　the　batch　production.　The　microchannel　has　the　same　Raman　spectra　as　that　of　the　PMMA　substrate.　The　spectra　shows　that　they　have　the　same　chemical　effect　on　the　polymerase　chain　reaction　(PCR)　mixture.　The　presence　of　the　bumps　of　resolidified　material　on　the　edges　of　the　microchannel　has　no　influence　on　the　hot-press　bonding　result　and　the　PCR　microfluidic　chip　could　satisfy　the　pressure　and　the　sealing　requirement　in　PCR　process.　An　amplification　of　a　DNA　template　with　180　bp　fragment　of　arabidopsis　thaliana　is　successfully　performed　with　this　chip,　in　less　than　30　min.　This　result　exhibits　the　availability　of　CO2　laser　direct-writing　ablation　technique　on　the　micromachining　of　the　PMMA　continuous-flow　PCR　microfluidic　chip.