In order to obtain fundamental knowledge of atomization, the three dimensional unsteady phenomena of pinch off were numerically studied by developed method. The numerical results of liquid shapes and velocity distributions were compared with the corresponding experimental ones. They showed satisfactorily good agreement in a qualitative sense. The liquid jet shape, the pressure and velocity distributions, and the inner flow structure were clarified through the comparisons of distinctly different flow fields due to presence or absence of surface tension. The condition of pinch off, which had close correlation with fluid acceleration at injection, was clearly specified. It was observed that the satellite drops were suppressed by large perturbation amplitude.