Abstract: This paper proposed a network security defense system to address the security risks of Wireless Local Area Network (WLAN) in railway station yard. It deeply analyzed the main security issues in WLAN of railway station yard at present, such as network eavesdropping, weak password protocols, and man in the middle attacks, sorted out the potential security risks that these issues may bring, and constructed an efficient security mechanism by adopting key technologies such as terminal security prevention and control, network authentication reinforcement, dynamic threat detection, and data transmission encryption, combined with a comprehensive strategy of institutional improvement and the combination of civil defense and technical defense to comprehensively enhance the security and stability of WLAN in railway station yard.