Abstract: Due to the limited working space, harsh environment and significant changes in geological conditions,tunnel engineering faces great difficulties in construction. The parallel operation in small-section tunnels is challenging,resulting in reduced efficiency in mucking transportation and strict requirements for machinery selection. This paper combines the construction example of a water supply project in Kenya to explore the application of the cantilever boring machine in the excavation and construction technology of small-section extra-long tunnels. The results show that the cantilever boring machine has advantages such as high excavation efficiency, fast tunneling speed, minimal disturbance to surrounding rocks, and strong applicability. It is easier to control the over-excavation and under-excavation amounts and ensure a favorable working environment inside the tunnel. Adoption of the cantilever boring machine is an applicable technology in small-section extra-long tunnel excavation.