Abstract: In the irrigation area of Chaishitan Reservoir in Kunming, the total length of main canals, main branch canals and main main branch pipes is 201.24 km. There are 15 main branch canals and 704 various canal systems, including 33 diversion tunnel projects and 37.33 km tunnel length. The tunnel section of this project is relatively small, involving small and extra-small section tunnels. According to the length of the tunnel, there are 14 short tunnels (L ≤ 500 m), 9 medium and long tunnels (500 m ＜ L ＜ 1 000 m), and 6 long tunnels (1 000 m≤ L ≤ 3 000 m) and 4 extra-long tunnels (L>3 000 m). The 6 long tunnels and 4 extra-long tunnels are basically on the key routes, which are the key points and diffi culties of this project. The research and application of the mechanized construction technology of small and extra-small-long tunnels in the diversion tunnel project has made the above-mentioned small and extra-small-section long tunnels Construction efficiency has been improved, construction environment has been improved, construction costs and project investment have been reduced, construction safety has been improved, and the construction period guarantee rate of this type of project in the entire project implementation process has been improved.