Gasoline direct injection (GDI) technology is admitted to be one of the most effective measures to improve the fuel economy for the spark ignition (SI) engines. Homogeneous Charge Compression Ignition (HCCI) combustion has advantages of low fuel consumption and ultra low NOx emissions. But the difficulty in the autoignition control and the narrow operation region inhibit the practical application of this technology. A hybrid combustion mode which combines SI mode and HCCI mode in separated working regions was regarded as a promising technology for HCCI engines. In addition, monitoring and providing feedback to the in-cylinder combustion characteristics is generally considered to be an effective method to improve and to optimize the combustion process. A lot of combustion information is included in the ion current generated by the in-cylinder combustion, and hence the ion current detection technique is considered to be a potential combustion feedback method. A strategy used in the SI/HCCI combustion mode switch based on ion current was established and experimented in a GDI-HCCI engine assisted by negative valve overlap (NVO). During the combustion mode switch process, by adjusting the key factors within the switch process, such as injection mass, injection timing and throttle opening, the switch process was optimized. The optimized SI-HCCI mode switch, not only the smoothness was improved, cylinder pressure amplitude, indicated mean efficiency pressure (IMEP), HC and NOx emissions were stable, but also the fuel economy and the emission performance were promoted.