Kuiqi No.2 tunnel is belonged to tender section A3 of the phase II project of Fuzhou International Airport Highway. It is the first small clear space tunnel project for 8 lanes in China with the span of 19.9 meters and with the middle rock pillar of minimum clear distance about 11.7 meters. According to the specialty of Kuiqi No.2 tunnel and based on discrete element method, some numerical simulation analysis is conducted to analyze the initial surrounding rock stress to the tunnel. The results show that the worst position of mechanical state in large-section tunnel is in the upper portion of middle rock pillar in weak surrounding rock, so special reinforcement measures should be used there. According to the reliability value of middle rock pillar in different rock mass, the net distance between Kuiqi No.2 small clear space tunnels with super span is reasonable to satisfy the stability requirement.