Abstract: The Yima No. 1 tunnel on the Yinchuan-Xi′ an high-speed railway passes through loess aquifer, the stratum is mainly composed of the soft and plastic loess. And it encountered such construction problems as water leakage, water inflow, softening of tunnel floor, increasing of water content in loess, failure of working face, decrease of rock mass stability and so on during tunnel construction. A experimental test on advanced ground dewatering was conducted, and the results show that by means of ground dewatering it can drain the underground water around main tunnel, reduce the risk of large amount water inflow and underground water pressure; after ground dewatering, the water content of loess decreases from 34.4 % to 27.2 % and the liquidity index decreases from 0.84 to 0.6, the physical properties and stability of loess rock mass are increased. The measured and monitored data show that accumulated crown settlements and deformation rate decrease significantly and the effect of ground dewatering is obvious.