To improve the thermal efficiency and inhibit the knock tendency of gasoline direct injection (GDI) engines, water injection technology has a bright application prospect. Utilize gasoline/water mixture as a way to realize this technology can lower the cost of modifying the engines and bring potential for better spray qualities. Hence it is essential to give deep insight into the effects of water on spray atomization, evaporation and mixture formation for gasoline/water mixtures. A spray synchronous measurement experimental system with a single hole nozzle is used to investigate the spray morphology, spray width and droplet size distribution of gasoline/water mixtures sprays under different water volume fractions (0 %, 20 %, 35 %) and different initial fuel temperatures (50 °C~ 130 °C). There are critical temperatures of 80 °C(G100), 100 °C(G80) and 120 °C(G65), above which the ‘collapsed’ spray appears. Noticeably, unlike the collapsed spray caused by jet-jet interactions in the multi-hole nozzles. In this article, the referred ‘collapsed’ spray has a smoother and more curved leading edge. The ‘collapsed’ spray pattern appears because finer droplets appear at high-temperature conditions and the aggregations of small droplets are rarer. The study of the spray width shows that the influence of water is two-sided and more evident under flash boiling conditions. The intensity of spray ‘collapse’ increases with fuel temperature and decreases with water volume fraction. Spray width variation within the axial of 5 mm is revealed by calculating heterogeneous nucleation rate and is mainly related to bubble growth and breakup under flash boiling conditions. The microscopic exploration demonstrates when spray enters flash boiling state, Sauter mean diameter (SMD) falls slightly. However, when fuel temperature reaches the critical temperature, spray enters ‘collapsed’ state and SMD drops drastically. For instance, when G80 spray transforms into flash boiling and ‘collapsed’ state, SMD decreases by 6.05 % and 61.43 % respectively.