The　experimental　research　of　homogeneous　charge　compression　ignition　(HCCI)　combustion　process　with　mixed　additives　was　carried　out　by　the　modified　fourth　cylinder　of　a　four-cylinder　diesel　engine.　The　influence　of　mixed　additives　on　the　HCCI　combustion　process　was　investigated.　Experimental　results　indicate　that　the　mixed　additives　are　better　than　the　single　additive　for　HCCI　fuel,　causing　ignition　and　heat　release　timings　to　be　advanced　and　the　peak　of　heat　release　rate　to　be　increased　at　different　engine　speeds　and　steady　operating　conditions.　Moreover,　with　the　increase　of　engine　speed,　the　influence　of　mixed　additives　on　HCCI　combustion　is　more　obvious.　In　addition,　mixed　additives　are　beneficial　to　improving　HCCI　engine　misfire　at　the　high　speed,　and　make　the　engine　operating　stable　at　specified　speeds.