Abstract: The paper structures the mathematic models for analyzing the phenomena of pulsed water-jet of a system embodied air-chamber was established with the method of the hydraulic transi-ent characteristic stream. The differential grid had three bounda-ries only, pulse source, air-chamber and nozzle, and none inte-rior node being needed. For the lengths of upstream and down-
stream sections may be unequal, using the novel Variable Time Step Method is necessary. The sample computation was show that, in order to induce an acceptable hydraulic resonance to strengthen pulsed water-jet. The air-chamber should be posi-boned correctly according to the concrete condition of the given system.

Key words: pulsed water-jet, air-chamber, hydraulic res-onance, hydraulic transient, method of characteristics, Variable Time Step Method