In recent years,because of the development of new underwater weaponwith long navigation time and distance,navigation reliability assessment method which based on success or failure often in tests is debated.One side,utilizing short navigation test data to assess reliability doesn’t consider the navigation time resulting in the low trustiness,on the other hand,performing adequate long navigation reliability tests is not only restricted on expenditure,development period and high risk,but also affected by the divorce from the other functionality and performance test,which brings about the low test efficiency and the insufficiency of data using.Therefor,based on the mission performing mode and combined with the exponential reliability distribution of underwater weapons,a method for actual navigation reliability test and assessment is proposed,which gives consideration to feasibility and practicability requirments and is adaptable to reliability engineering practice of underwater weapons.