One of the important challenges for modeling Direct Injection Spark Ignition gasoline engine is flash boiling spray. Flash boiling occurs when the ambient pressure is lower than vapor pressure of fuel. It affects spray structure and mixture formation process inside engine. Gasoline is multi-component fuel and effects of each component on flash boiling is hard to estimate. As a pre-research for mixture formation process of flash boiling spray, single component fuel was used to validate flash breakup model. Spray visualization was conducted for varying fuel temperature and ambient pressure. Simulation was carried out using KIVA 3V release2 which flash breakup model is applied to. Bubble growth in drop was modelled by Rayleigh-Plesset equation. When bubbles grow to satisfy breakup criterion, breakup occurs and induces smaller SMD for flash breakup cases. Analysis of mixture formation inside engine was carried out for low load condition using flash breakup model. Also simulation without flash breakup model was conducted to analyze the effects of flash breakup model. Though the further improvement of flash breakup model should be conducted, analysis which includes flash breakup model shows improved in-cylinder mixture formation and combustion process in engine simulation compared to experimental results.