From one perspective, tighter security screening has the benefit of deterring adversary passengers and enhancing safety. However, this approach can also produce congestion problems for normal passengers. Adapting to screening policies, both adversary and normal passengers decide their application strategies to the security system to maximize their payoffs, which in turn affects the security agent's payoff. This paper integrates game theory and queueing theory to analyze an N-stage imperfect screening model that considers reject or pass decisions, in which applicants have the chance to be passed or rejected at each stage of the system. An imperfect three-stage screening model is numerically illustrated. Furthermore, the application probabilities, screening probabilities and approver's payoff as functions of the number of screening stages are analyzed. This paper provides some novel insights on screening policies and the optimal number of screening stages which would help security screening policy makers.