The construction of subsea tunnels crossing deep weathered slot is unprecedented in China. Geology forecasting technology, monitoring and measurement technology, advance full face deephole grouting technology, advance pipe roof reinforcement technology and other assistant construction technologies are adopted, after 9month research and practice, for the construction of the service tube of Xiang'an subsea tunnel in Xiamen crossing  F1 deep weathered slot. In addition, NATM (New Austrian Tunneling Method) is strictly implemented during excavation and support. Owing to all the above measures, the 90mlong F1 subsea deep weathered slot, which has great risks, is conquered. The construction technology of the service tube crossing F1 subsea deep weathered slot is presented in the paper, which can provide reference for similar projects in the future.