Aiming at elucidating the relationship between injection conditions, especially injection velocity profiles, and atomization characteristics of liquid sheet at the impingement type of injector, numerical analysis, experimental observation and theoretical analysis were carried out. For computing atomization phenomena, a numerical method has been developed. The method was verified through quantitative comparisons with corresponding experiment of pinch off. Then experimental and theoretical studies were performed on atomization of axisymmetric liquid sheet, which was produced by collision of two water jets in opposite direction. The numerical results of the atomization process through Kelvin-Helmholtz type of instability showed qualitative resemblance with corresponding theoretical analyses. It was clarified that non-uniform injection velocity profile resulted in velocity distribution with inflection point inside the sheet. Thus the sheet with non-uniform injection velocity profile tended to be unstable and enhanced atomization. The effect of injection velocity profile on atomization at the impingement type injector was also represented.