The combat effectiveness of reconnaissance UAV depends on the joint control of both enemy and us. In order to study the factors that affect its combat effectiveness, the combat failure process and the influence trend of the factors change on the combat failure, the methods of combat effectiveness analysis and composite factor space characterization are proposed. Firstly, the combat effectiveness and its influencing factors are studied. Then, the evolution process of UAV combat failure is studied from concept description, topological abstraction and mathematical calculation. The game analysis method of combat effectiveness is put forward and the composite factor space is constructed. The research shows that the evolution process of combat failure can represent the change of combat effectiveness. The system failure evolution model can be used to construct the evolution process of UAV combat failure. The topology abstraction uses the space fault network model to obtain the network topology of the combat failure process. The mathematical model is established by the characteristic function, and the probability distribution of each event can be calculated. The example shows the process of analysis and obtains the probability distribution of all events in the combat failure process. This method analyzes the combat failure process of UAVs from the aspects of concept, topology, and mathematics, and constructs a composite factor space to represent the combat failure situations of both sides. Finally, the general properties of the research method are explained, as well as its existing shortcomings and solutions.