Abstract: To enhance the reliability of data transmission in seismic networks and mitigate service interruptions caused by single-point link failures, this study designed and deployed a high-availability dual-link transmission system at 14 reference stations of the Shanghai Earthquake Early Warning Network. The system adoidopts an "MSTP optical fiber primary link + 5G wireless backup link" architecture. The primary link relies on a 2 Mbps MSTP (Multi-Service Transport Platform) dedicated fiber line, offering inherent low latency and high stability for core data transmission. The wireless backup link utilizes China Broadcasting Network's 700 MHz 5G network, which provides extensive coverage and strong signal penetration. By incorporating a dedicated DNN (Data Network Name) and wireless network slicing technology, an end-to-end logical channel isolated from public networks is established, ensuring transmission security and quality for the backup path. To enable intelligent redundancy and seamless failover, the architecture integrates IPsec tunnel encryption with the OSPF (Open Shortest Path First) dynamic routing protocol. Through differentiated OSPF cost settings and persistent link-state monitoring, the system achieves automatic sub-second switching to the 5G backup link upon failure of the primary fiber link. Operational experience, including performance during extreme weather, confirms that the system significantly improves station availability and data transmission resilience. This solution offers a practical and replicable approach for enhancing communication assurance in earthquake early warning systems and other critical infrastructure applications.