In order to avoid the safety problem caused by dud in the actual naval gun combat training, the security of dud left in the bore was studied. Analyzes the mechanism of dud left in the bore, studies the changes of explosive sensitivity and bore temperature conduction that affect the safety of bore ammunition, and makes a simulation analysis of the temperature change process of typical dud left in the bore with SolidWorks software. The results show that, with the change of time, chamber can’t be exploded and the propellant can’t be ignited, according to the comprehensive judgment of historical experience, the exclusion waiting time of the dud left in the bore is relatively safe after 30 s is selected.