Flash boiling was easy to happen at high fuel temperature and low ambient back pressure when direct injection was used. Flash boiling spray had an application prospect because it had short penetration and easy spray and could reduce exhaust emission and improve fuel economy. However, the application of turbocharger led to difficult flash boiling due to the increase of intake pressure. In view of this phenomenon, it was proposed to promote the flash boiling spray by adding the low boilingfuel to the high boiling fuel after studying the mixed fuel distillation characteristics. Test fuels were a series of blended fuel which was composed of the low boiling point fuel like isopentane and the high boiling fuel like n-undecane and their distillation characteristics were studied through the distillation test. Finally, the morphology changes of mixed fuel were studied by taking the Mie scattering diagram of fuel spray at different fuel temperatures and environmental back pressures inside constant volume bomb. The results show that the mixed fuel cannot be boiled to produce distillate at one boiling point like single fuel but in a certain temperature range. It is a three-stage distillation curve. The low boiling point fuel first produces during the distillation because of its evaporation. The macroscopic measurement results show that the method can realize the flash boiling state at high back pressure and 40% volume fraction is the best adding proportion. Besides, adding low boiling fuel to higher temperature fuel is beneficial to flash boiling.