Reliability is an important metric for unmanned aerial vehicles (UAVs) to perform important, complex, and dangerous tasks. In addition, reliability influences the operational cost in UAVs routing. In order to reduce the operational cost of UAVs tasks, a method of routing strategy optimization is proposed from a view of mission reliability in this paper to address the limitations in routing scheduling. Different from previous studies on the UAVs routing optimization problem, this paper proposes a method that can reduce the operational costs of UAVs tasks based on the mission reliability. This method includes two stages: the pre-optimization stage and the rescheduling stage. In the pre-optimization stage, an optimal UAVs route solution is obtained for all the targets, while in the rescheduling stage, new UAVs are dispatched to the unvisited targets in the pre-optimization stage based on the new optimal UAVs route.