The multi-hop wireless sensor network is a type of data acquisition and transmission technology, which has wide application prospects in bridge detection systems. To achieve efficient and reliable data transmission, the media access control (MAC) protocol is essential. The purpose of this study is to evaluate the performance of different MAC protocols in bridge detection systems on multi-hop wireless sensor networks. By comparing several commonly used MAC protocols, we analyzed their differences in data transmission delay, energy efficiency, and network capacity. First, we simulated the multi-hop wireless sensor network in a bridge detection system by establishing a network model. Then, we selected several common MAC protocols as evaluation objects, including CSMA/CA, TDMA, and ALOHA. We simulated different practical application scenarios by setting different parameters and scenarios in the network model. Through the analysis of the experimental results, we found that there are some differences in the performance of different MAC protocols. The CSMA/CA protocol performs well in terms of data transfer latency, but poorly in terms of network capacity and energy efficiency. The time division multiple access (TDMA) protocol performs well in terms of network capacity and energy efficiency, but is sensitive to data transmission delays. The ALOHA protocol performs poorly in terms of network capacity, but can provide a lower data transfer latency. On the basis of the evaluation of the performance of these protocols, the following conclusions are drawn. For multi-hop wireless sensor networks in bridge detection systems, it is very important to choose a suitable MAC protocol. The CSMA/CA protocol is a good choice in application scenarios that require real-time responses, whereas the TDMA protocol can provide higher network capacity and energy efficiency when no data transmission latency is required. In addition, note that the performance of the MAC protocol may vary under different network loads and topologies. Therefore, in practical applications, it is crucial to choose the right MAC protocol according to the specific situation. In summary, in this study, we provide reference and guidance for selecting a suitable MAC protocol by studying the performance of multi-hop wireless sensor networks in bridge detection systems. Our research results are of great significance for improving the data transmission efficiency and reliability of bridge detection systems.