Abstract: 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 HCCl combustion can be obtained, but the gasoline cannot burn without additives.