Abstract: The middle rock pillar is a key component for the stability control of the surrounding rocks in tunnels with small clear distance, and it is a major challenge in the engineering design and construction process to distinguish the safety of the middle rock pillar. This paper establishes the mechanical analysis model of parallel tunnels with small clear distance under Class IV surrounding rock conditions by analyzing the failure modes of the middle rock pillar under different surrounding rock grades and buried depths, and identifies the location of the fracture surface of the middle rock pillar. This paper divides the upper sliding block of the middle rock pillar into two cases according to the different shapes, derives the calculation formulas of the slip resistance, sliding force and safety coefficient of the upper sliding block of the middle rock pillar according to the principle of slope stability, the assumption of ultimate equilibrium and Protodyakonov′s compressive arch theory, so as to establish the safety coefficient meth? od to evaluate the safety of the middle rock pillar and verify it by introducing numerical simulations. The verified safety coefficient method is then applied to an actual tunnel project to evaluate the safety of the middle rock pillar,which concludes that the critical thickness for the tunnel middle rock pillar failure is 6 m. Middle rock pillar sections with thickness below 6 m are then reinforced using anchor bolts.