Flash boiling spray is effective in improving the atomization and evaporation characteristics for gasoline direct injection engines. However, for a multi-hole injector, spray collapses with both long penetration and a narrow spray angle above certain high superheat degree, which deteriorates air/fuel mixing and hence increases emissions. It is therefore not desired for engine applications while the mechanism of spray collapse still remains unclear. In the present study, key physics involved in flash boiling, including bubble formation, bubble growth, as well as bubble breakup are added to the traditional spray model in KIVA-3V to describe the development process of flash boiling spray and the simulation of a multi-hole injector spray characteristics agrees well with experimental observation under various conditions. On the spray collapse phenomenon, it is found that the low pressure regions play a critical role through affecting the velocity field and thereby resulting in spray structure transition. The low pressure regions are observed at the position where entrainment effect takes place. With fuel temperature increasing, the drop of pressure in low pressure regions is big enough to move the droplet toward to spray center and hence the spray collapses. The spray structure transformation mainly depends on the pressure in the low pressure regions. Eddies are observed in the low pressure regions and a larger pressure difference corresponds to a larger eddy. When flare flash boiling occurs, although the overall evaporation intensifies greatly, the vapor is relatively confined in the spray center due to spray collapse, which is undesired for fuel/air mixing.