The Weihe Tunnel on BaojiLanzhou Passengerdedicated Line passes through the Neogene mudstone for a long distance in Tianshui, Gansu. The strength and stability of rock are poor and the infiltration of the river has great influence on the construction and operation of the tunnel. In order to put forward reasonable tunnel construction countermeasures, the compressive strength, compression deformation, expansibility, disintegration and water permeability of the Neogene mudstone in Tianshui, Gansu are carried out by laboratory tests. The results show that: 1) The Neogene mudstone is extremely soft, which is not expansibile but is with disintegration after water absorption. 2)The infiltration coefficient of the Neogene mudstone is very small, which belongs to the micropermeable stratum, and the water separation effect is good. During the tunnel construction, nonblasting excavation methods are recommended and the formation displacement is strictly controlled. The principle of strong support and early closure should be followed and the surrounding rock should not be soaked by construction water.