This paper illustrated the instability mechanism of tunnel face in sand stratum under water by using the theory of Mohr-coulomb yielding criteria and the NITM method on the background of the second JiuHe tunnel in the railway from LanZhou to ZhongChuan airport. The drainage measures were taken to deal with the water in the stratum before tunneling and deep-hole pre-injecting measures were taken to improve the strength and stiffness of stratum. The double temporary invert and temporary sheeting were setup to provide artificial restriction for tunnel to improve the stability of tunnel.