Combined with the current research situation of construction of tunnels with small clear spacing, the key technology of design and construction of tunnels with small clear spacing is summarized, which primarily consists of rational clear interval of tunnels with small clear spacing, advanced support, construction methods and clip rock reinforcement. The passage describes various methods of key technologies currently in use and the selecting rule under the condition of various categories of surrounding rocks, which has some significance on the safe construction of tunnels with small clear spacing.