In order to deeply study the spray characteristics of porous gasoline direct injection engine （GDI） injector under the conditions of cold injection and flash evaporation， a constant volume spray chamber test platform was built with GDI injector and self-made high-pressure fuel injection control system. The real-time control experiments of fuel injection process were carried out for the spray characteristics under three typical flash evaporation conditions. The evolution characteristics of the two-dimensional macro morphology and three-dimensional spatial structure of ethanol gasoline flash spray under different injection pressures were studied. The results show that the structure of flash spray is mainly determined by ambient pressure and fuel temperature； Lower atmospheric pressure and higher fuel temperature will accelerate the flash evaporation process； The higher the injection pressure， the faster the injection process， the longer the spray penetration and the lower the collapse degree， and the lower the injection pressure， the higher the penetration force at the tip of the injection process. It is concluded that the formation law of the flash spray of the porous GDI injector can provide a technical reference for improving the performance of the vehicle engine.