Numerical　simulation　on　the　effect　of　additive　(DTBP)　on　HCCI　ignition　was　taken　by　using　the　single-zone　model　coupled　with　a　detailed　kinetic　model.　The　results　show　that　the　base　fuel　with　additives　will　improve　the　HCCI　combustion　remarkably.　The　ignition　timing　advances　with　the　increase　of　DTBP　mass　fraction.　However,　over-addition　of　the　additive　is　unfavorable　to　engine　operation.　In　order　to　achieve　the　best　performance　at　low　engine　load,　the　mass　fraction　of　DTBP　additive　in　PRF90　needs　to　be　increased　with　the　increase　of　engine　speed.　The　HCCI　combustion　characteristics　were　sensitive　to　the　changes　of　engine　operating　parameters.　Increasing　in　intake　temperature,　in　intake　pressure　and　in　compression　ratio　causes　an　early　combustion　while　increasing　in　engine　speed　postpones　the　combustion.