Using the kinetic energy equations and the routine sonde data, each term in the synoptic scale, subsynoptic scale and nonlinear interaction kinetic energy equation is respectively calculated in this paper in order to analyze the main dynamical processes in the "96.8" torrential rain event. The results show that there exist nonlinear interactions between synoptic and subsynoptic systems in the event. By which the kinetic energy of the synoptic system is reduced and that of the subsynoptic system is increased. In other words, the synoptic system acts as a source of kinetic energy for the subsynoptic system to grow the torrential rain system.