Abstract: The occurrence and development characteristics of concrete cracks are important characterization parameters of concrete health. Given that steel reinforcement is the inherent structure of concrete, this paper proposes a method for monitoring cracks in concrete using steel reinforcement antennae. In this method, a steel reinforcement transmitting and receiving antenna pair embedded in concrete is set, and the cracks in concrete are detected according to the amplitude of the antenna pair' parameter S₂₁ that can reflect electromagnetic wave propagation. To this end, a simulation model based on the CST Studio Suite software was constructed to calculate the amplitude of S₂₁ using the software. The relationship between the amplitude of S₂₁ and the crack state was analyzed. The results show that the state of cracks in concrete has a significant impact on the amplitude of S₂₁, and thus the cracks can be detected according to the characteristics of the amplitude of S₂₁. The cracks can be identified if the ratio between the amplitude of S₂₁ obtained using the models with and without cracks exceeds a certain threshold. Meanwhile, the corresponding frequency band that can identify the cracks is defined as the characteristic frequency band of cracks. The simulation results show that the amplitude of S₂₁ significantly changes with different crack thickness, crack angles, and crack positions. Therefore, the concrete cracks and their characteristics can be judged from the amplitude of S₂₁ by setting up a steel reinforcement transmitting and receiving antenna pair in concrete.