Launch flight reliability is an important tactical index of missile. Considering that the flight test data cannot meet the high reliability requirement of missile， this paper proposes a missile reliability evaluation method based on reduced factor Bayes theory， by integrating the ground data. This method first converts the ground test data and the consistency check is carried out； then， using L-M method to convert ground data into prior information of missile flight test. Finally， the lower limit of missile launch flight reliability is evaluated based on the reduced factor Bayes theory. The results of a typical case study show that the proposed method can make full use of reliability evaluation data of the missile and its subsystem， which not only reduces the cost and risk of flight test， but also increases the rationality of the missile launch flight reliability evaluation.