Compared with single-layer attacks, cross-layer attacks in wireless ad hoc networks can better conceal attack behavior, achieve better attack effects, or reduce the cost of attack. In order to detect cross-layer attacks in wireless ad hoc networks, a detection model based on game theory was proposed. As the attack will inevitably affect the parameters of each protocol layer, the corresponding strategy matrix and payoff matrix was built from the aspect of attack-defense game of protocol layer, and the mixed strategy Nash equilibrium solution was obtained by equilibrium analysis. Simulation experiments results show that the detection system adopting mixed strategy can achieve a better detection performance and save the energy consumption significantly, compared with the traditional detection system.