In order to meet the demand of emergency communication data transmission outside nuclear power plant, the application research of long-distance non relay transmission technology of optical fiber is carried out. Firstly, the paper introduces the limited factors and safety factors of long-distance relay free transmission of optical fiber, and points out the solutions respectively. Then, a long distance relay free optical transmission method without remote optical pump amplifier(ROPA) is proposed and verified by experiments. The experimental results show that the non relay transmission distance of optical fiber link is 252.15 km, which can meet the requirements of ultra long distance data transmission and safety of emergency communication command network of nuclear power plant.