Abstract: To compensate the shortage of working reliability assessment of a torpedo in sea trial with indistinguishable long range and short range based on the conventional binomial distribution, a new assessment method based on the Weibull distribution is proposed. The features of modern torpedoes, such as complex system structure and fault states, larger range, and longer working time, are considered in this method. Example shows that the new method is simple and practical, and it can assess working reliability of a torpedo more intuitively and scientifically. This method may be applicable to reliability assessment of modern torpedo in sea trial