A high pressure direct injection gasoline injector with 50 MPa was designed and developed. The relationship between the spray characteristics of injector and the injection pressure was then studied on a constant volume bomb. The effects of 50 MPa high pressure and direct injection technology on the combustion process and emission were further studied on a single-cylinder optical engine of homogeneous charge and direct injection by using combustion analysis and high-speed photography. The results show that increasing the injection pressure to 50 MPa can still decrease the spray particle size and improve the fuel and air mixing process compared with the current 35 MPa in-cylinder gasoline direct injection system. It can greatly reduce the emissions of unburned hydrocarbons and particulate matter especially in the medium and high loads, which shows certain potential application value.