Mountain tunnels bored by tunnel boring machines(TBMs) at high water levels often encounter issues, such as joint leakage and cracking. Therefore, a novel drainage technology incorporating pressure relief valves are proposed to address these challenges and protect the surrounding groundwater environment. This technology aims to control the drainage volume and reduce groundwater pressure behind tunnel linings. First, a field test is conducted in the Daxiangshan tunnel on the FuzhouChangle airport intercity railway. The results indicate that with a drainage hole spacing of 3 m and the relief valve pressure set to zero, the water pressure behind the segmental lining can be effectively reduced to 30% of the hydrostatic pressure. Furthermore, the groundwater drainage volume is maintained at 3.144 m3/(d·m). Second, a hydraulic coupling numerical calculation model is established by integrating a pressure relief drainage unit. Here, a pressurerelief valve is installed in the arch foot drainage hole. The numerical results are compared with field test data, maintaining a relative error of less than 8%. Finally, a parameter analysis is performed to examine the effects of the drainage hole spacing and relief valve pressure on the tunnel water drainage volume and the water pressure behind the segmental linings. The findings are as follows: (1) Reducing the tunnel drainage hole spacing from 15 m to 3 m increases the water pressure reduction rate at the invert from 40% to 78% and increases the water drainage volume from 1.284 m3/(d·m) to 3.362 m3/(d·m). (2) With a drainage hole spacing of 3 m, increasing the valve pressure from 0 to 800 kPa reduces the water drainage volume from 3.362 m3/(d·m) to 0.678 m3/(d·m). Concurrently, the groundwater pressure on the segmental lining increases linearly, and the water pressure at the invert shows a significant variation, with the growth rate increasing from 0% to 77%.