Aiming at clarifying and quantifying atomization characteristics at impinging jet injector, numerical analysis, experimental observation and theoretical analysis were conducted. For computing atomization phenomena, a numerical method was 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, as well as numerical analysis. The numerical results of the atomization process through Kelvin-Helmholtz type of instability showed qualitative resemblance with experimental visualization and theoretical analysis. Finally, atomization characteristics at impinging jet injector were numerically analyzed. Liquid distributions from the injector face plate were quantified, and the dynamic behavior of the liquid sheet was found to affect strongly on liquid distributions at downstream.