Effects　of　driving　gas　pressure　on　measurements　of　ignition　delay　times　of　dimethyl　ether　(DME)/oxygen/nitration　mixture　and　methane/(CH4)　oxygen/argon　is　studied　in　a　rapid　compression　machine　(RCM).　With　a　certain　initial　temperature　288K,　experiments　are　conducted　with　driving　gas　pressure　of　0.21　to　0.65MPa,　initial　pressure　of　0.06　to　0.12　MPa　and　compression　ratio　of　10.65　to　13.75.　The　results　shows　that　the　appropriate　driving　gas　pressure　should　be　chosen　according　to　the　range　of　initial　pressure　and　the　design　features　of　different　rapid　compression　machine　to　avoid　the　rebound　of　piston.　Also,　with　a　low　driving　gas　pressure,　the　top　dead　center　(TDC)　cannot　be　accurately　defined　due　to　the　coupling　of　the　first　ignition　delay　and　the　low　temperature　combustion　of　DME/O2/N2　mixture　in　the　process　of　compression.　Additionally,　both　the　first-stage　and　overall　ignition　delays　of　DME/O2/N2　mixture　shorten　with　decreasing　driving　gas　pressure　due　to　its　low　auto-ignition　temperature,　moreover,　the　ignition　delay　is　much　more　influenced　by　the　change　of　driving　gas　pressure　with　decreasing　compression　ratio.　In　contrast,　under　different　ignition　delay,　whether　long　or　short,　the　ignition　delay　of　CH4/O2/Ar　mixture　is　insensitive　to　the　change　of　driving　pressure　within　a　certain　range　due　to　its　high　auto-ignition　temperature.