This paper has modeled the reliability of surveillance mission with unmanned aerial vehicles (UAVs). In order to surveil a number of targets, some UAVs can be assigned to visit the targets. It is assumed that if a UAV is shot down during the mission all the targets assigned to the UAV cannot be surveilled. The mission is regarded as successful if all the targets are assigned and successfully surveilled. An optimization framework is presented to solve the UAV routing plan with the consideration of mission reliability.