Natural　gas　(NG)　direct　injection　(DI)　technology　benefits　the　engine　with　high　efficiency　and　clean　emissions,　and　the　high-pressure　gas　fuel　injection　process　causes　crucial　effects　on　the　combustion.　This　study　presents　an　optical　experimental　investigation　on　the　high-pressure　methane　single-hole　direct　injection　and　premixed　ignition　combustion　based　on　a　visualization　cuboid　constant　volume　bomb　(CVB)　test　rig.　The　experimental　results　show　that　the　methane　jet　process　is　divided　into　two　stages.　The　methane　gas　jet　travels　at　a　faster　speed　during　the　unstable　stage　I　than　that　during　the　stable　stage　II.　The　injection　pressure　causes　more　influence　on　both　the　jet　penetration　distance　and　the　jet　cone　area　during　stage　II.　The　methane　jet　premixed　flame　is　a　stable　flame　with　a　nearly　spherical　shape,　and　its　equivalent　radius　linearly　increases.　The　methane　jet　premixed　flame　area　also　increases　while　the　flame　stretch　rate　declines.　The　methane　jet　premixed　flame　velocity　rises　as　both　the　standing　time　and　equivalent　ratio　increase.　The　methane　jet　premixed　flame　is　a　partial　premixed　flame,　and　the　peak　of　the　methane　jet　premixed　flame　occurs　at　greater　equivalence　ratio　phi,　i.e.,　phi　＞　2.　As　the　injection　pressure　rises,　the　jet　premixed　flame　equivalent　radius　increases,　and　the　flame　velocity　linearly　increases.　The　higher　the　methane　injection　pressure,　the　faster　the　jet　premixed　flame　velocity.