Abstract: Aiming at the recovery and reuse of a dummy torpedo in torpedo test, this paper discusses the unloading time to ensure the dummy torpedo against getting to the see bottom. By analyzing the parameters about torpedo’s entering water, weight and hydrokinetic parameters, practical simulation conditions are provided. Based on the precondition of ignoring unload impulsion and adaptability of hydrokinetic parameters to torpedo equation at low speed, the uncontrolled trajectory of dummy torpedo is simulated and analyzed. For the given reference sea, two depth curves of unloading and without unloading are calculated and compared. The resistance coefficient is empirically estimated to increase by two times after unloading, hence the unloading time for dummy torpedo not to sinking into the see bottom is eventually gained.