Gasoline Partially Premixed Combustion (PPC) is an advanced combustion concept to simultaneously reduce the NOx and soot emissions whilst retaining high engine efficiencies. In order to have a better understanding of gasoline PPC operation in terms of mixture formation, combustion and emissions characteristics, the investigation was carried out at 1200 bar injection pressure using the combination of thermodynamic and optical diagnostic analysis in a single cylinder common rail fuel injection engine with optical access. The PPC operation was achieved with a combination of high dilution and higher intake charge temperature at part-load condition using primary reference fuel (PRF). Split injections of two fuel distribution strategies (50:50 and 70:30) were studied. Based on the thermodynamic analysis of the engine performance, the high speed imaging technique was employed to observe fuel spray development and combustion process, while the simultaneous Mie-LIF technique was developed and utilized for the visualization of fuel liquid and vapour formation. The results showed that better performance can be obtained when the combustion phasing (CA50) was properly controlled by injection timings. Simultaneous reduction of NOx and soot emissions were achieved under gasoline PPC operations with the penalty of excessive uHC emissions. 50:50 injection split strategy produced less soot emissions than the 70:30 strategy. The Mie-LIF results illustrated the faster fuel evaporation process of gasoline PPC than diesel operation, while more luminous combustion was observed in baseline diesel combustion using high speed imaging.