Abstract: Using the inflow at K23+708 of the extra-long Feixianguan tunnel on the Yakang highway as an example, the formation mechanism of the water inflow was analyzed based on data from site investigations, monitoring and statistics regarding the time-history characteristics of the inflow; it was determined to exhibit a“combination of draining and blocking with limited discharging.”A comprehensive treatment scheme is put forward that includes temporarily reinforcing the deformed primary support, draining the ground water, employing peripheral grouting with condulets and strengthening the stiffness of inverted arch and lining.