Excitation of the longitudinal modes of hull by the fluctuating thrust from propeller-shafting system is a major source of the radiated noise at low frequencies of submarines. Based on the four-pole parameters method, a simple model for analyzing the axial vibration of submarines is proposed, which accounts on the elasticity of the hull, thrust bearing and shafts. The axial transmission of powerflow from shafting to the hull is investigated. It is found that the fluctuating thrust will induce resonances of the shafting and the hull because they are elastically coupled, which will result in powerflow peaks. Such resonances are more significant while their frequencies are around the axial modes of the shafting. Dynamic vibration absorbers are designed to depress such powerflow peaks. It is found that absorbers could reduce the powerflow more effectively when they were tuned to resonances around the axial modes of shafting than tuned to others.