Abstract: In order to reveal the influences of high pressure fuel injection system on the performance including fuel consumption and exhaust emissions of gasoline direct injection(GDI) engines,the spray characteristics of high pressure swirl type of GDI injector were investigated experimentally and numerically.The experimental analyses had been carried out that the fuel injection into a constant volume chamber within different ambient pressures was visualized by high speed complementary metal oxide semiconductor(CMOS) camera.The spray development,spray penetration,spray cone angle,spray tip velocity and droplet characteristics were measured at various injection pressure,ambient back pressure and at different injection durations.Experimental results show that under the low back pressure ambient conditions,the spray comes out a hollow cone with wide spray angle and initial spray slug at the tip which meet the mixing control concept of homogenous mixture preparation,while the spray exhibits a solid compact cone under high back pressure which satisfy the stratified mixture preparation concept.An obtained empirical equation for spray penetration is validated by experimental results.Vortexes in the opposite direction exist in the rear part of the spray under low back-pressure ambient conditions while the vortexes form in the middle part under high ambient pressure ambient conditions.