In view of the LPAR (large phased array radar) system has too much safety factors and it is difficult to evaluate. Firstly，the LPAR safety evaluation index system based on the radar characteristic was analyzed and established. Secondly, a method to determine the comprehensive weight based on the improved FAHP(fuzzy analytic hierarchy process), entropy weigh and Lagrange algorithm was put forward, and the safety fuzzy comprehensive evaluation model was established. Thirdly, taking safety evaluation of the certain LPAR system as an example, the safety comprehensive weight of the LPAR system was determined by the proposed method, the safety evaluation was carried out by the established model. Finally, this method is compared with the traditional AHP method, and the feasibility and rationality of the method are verified.