The high speed long-haul optical transport network faces enormous challenges in improving unrepeatered transmission distance. According to the results of abundant experiments and practical researches, the large-effective-area design of G.654.E optical fiber increases the size of the fiber core region, which enables higher power of optical signal to be propagated. Therefore this kind of fiber can extend optical transmission distance by 70% – 100% compared to the G.652 optical fiber. It is proven that G.654.E fiber can extend the transmission distance of relay nodes up to 900 km or more. And a field experiment demonstrates that G.654.E single-mode fiber can achieve 2000km WDM transmission distance of 400 Gbps combined with erbium-doped fiber amplifier (EDFA) and backward distributed Raman amplifier (DRA).