Abstract: Conventional reliability assessment method of undersea vehicle navigation mission regards incomplete course statistics as whole course statistics, which does not meet the requirements of the specification profile. In view of the shortcomings of conventional assessment methods, a comprehensive assessment method is proposed, which the navigation process is considered to be an exponential distribution of life, and the time of actual navigation is counted and converted into a mission equivalent number according to the time of the whole course. Combining with other subsystems’ trial data, the L-M method is used to calculate the number of times and the number of failures of the total sea trial task. The smallest acceptable value of mission reliability is calculated with the lower confidence limit method based on the binomial distribution for determining whether the reliability of the task meets the requirement. It is concluded that the proposed method solves the shortcomings of the conventional assessment method, and is easy in implement, simple in operation, and reliable in assessment, and this method can greatly reduce the number of trial times and improve the efficiency of trial.