Abstract: To enhance the reliability of data transmission in seismic networks and mitigate service interruptions caused by single-point link failures, a high-availability dual-link transmission system was designed and deployed at 14 reference stations in the Shanghai earthquake early warning network. The system adopts 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 inherently 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 was established to ensure transmission security and quality for the backup path. To enable intelligent redundancy and seamless failover, the architecture integrates IPSec tunnel encryption with an OSPF (Open Shortest Path First) dynamic routing protocol. Through differentiated OSPF cost settings and persistent link-state monitoring, the system achieves automatic subsecond switching to the 5G backup link upon failure of the primary fiber link. Operational experience, including performance during extreme weather conditions, confirmed that the system significantly improved station availability and data transmission resilience. This solution offers a practical and replicable approach for enhancing communication assurance in earthquake warning systems and other critical infrastructure applications.