Abstract: Subsea Electronic Modules (SEM) are critical equipment for offshore oil and gas development. Existing domestic SEM communication systems are hampered by low reliability and inadequate redundancy. To tackle these problems, the authors proposed a communication scheme based on Layer 3 industrial switches. The communication links were divided into the subsea segment between topside master control stations and SEMs, and the downhole segment linking SEMs to terminal devices. Modbus TCP/IP and Virtual Local Area Networks were adopted for logical isolation to avoid network storms and data security risks.Fiber-optic self-healing ring network, link aggregation and routing priority were integrated to build multi-redundant communication architectures and resolve single-point failures. The VxWorks real-time operating system and Tornado development environment were deployed to ensure robust system operation.Simulations and calculations show that the total system latency is merely 1.165 ms for an 18 km transmission distance, and the fiber communication margin is between 16.196 dB and 21.196 dB. Power line communication features stable attenuation under harsh conditions, while DSL works compatibly with current subsea production systems. Practically applied in laboratories and oilfield facilities, this scheme maintains stable communication under extreme temperature and vibration. It supports seamless automatic fault switching and fully meets the communication demands of ultra-deepwater subsea production systems.