In oil and gas extraction, coiled tubing technology has attracted much attention because of its advantages such as fast operation time, little damage to the formation low labor intensity, etc. The research of coiled tubing technology is a systematic project involving many aspects. This paper first starts the discussion from the domestic and international literature published and the main research scholars review the development process of coiled tubing technology, and summarise the relevant achievements existing in China. At present, the coiled tubing technology is in the stage of rapid development, but the research of coiled tubing in ultra-deep wells is minimal. The authors describe the relevant research carried out by the team on the downhole accessibility of coiled tubing in ultra-deep wells, the extension of the horizontal section of coiled tubing, the optimization of the construction parameters of coiled tubing operation, and the downhole safety assessment of coiled tubing operation. According to the current status of coiled tubing technology research in ultra-deep wells, it is suggested to carry out the research related to the real-time warning technology of coiled tubing fatigue life based on the digital intelligence technology, the ability of tractor?driven coiled tubing extension, and the research and development of high?temperature?resistant tools and fluids, to solve the technical difficulties of coiled tubing operation in ultra-deep wells.