For　the　problem　of　misfire　of　the　HCCI　engine　at　low　load,　the　engine　test　is　carried　out　by　mixing　proper　ignition　improver　(C6H5CO-O-O-C(CH3)3)　with　the　reference　fuel　(90%iso-octane　+　10%　n-heptane)　and　the　RON　93　gasoline　respectively.　After　mixing　C6H5CO-O-O-C(CH3)3　of　0.3%-1.2%　in　mass　fraction,　compared　with　the　reference　fuel　result,　the　engine　operation　range　is　enlarged　by　15%-28%　at　low　load　and　reduced　by　0.5%-0.7%　at　high　load.　It　shows　that　additives　can　increase　operational　range　of　engine　at　low　load,　while　decrease　it　at　high　load　at　the　same　time.　When　proper　additive　is　mixed　with　RON　93　gasoline,　stable　HCCI　combustion　can　be　obtained,　but　the　gasoline　cannot　burn　without　additives.