It is believed that, due to the ignorance of the engineering geological characteristics of Tertiary strata, there are great risks in the construction of tunnels located in Tertiary strata. In the paper, the property of Tertiary strata are investigated by means of exploration, laboratory test and insitu test, on basis of the investigation and design of Zhongtiaoshan tunnel on Menghua railway. Conclusions drawn are as follows: The Tertiary strata at the southern foot of Zhongtiaoshan mountain can be classified into moderatelycemented conglomerate, weaklycemented conglomerate, weakdiagenetic sandstone, semidiagenetic mudstone and semidiagenetic sandy mudstone; The strata has such characteristics as low diagenesis degree, being easy to be weathered after exposure and being easy to be softened when water is encountered; the mudstone and sandy mudstone have swelling property; the hydrogeological characteristics of Tertiary strata depends on the lithology; collapse, serious deformation, water inrush and sand inrush are common risks during tunnel construction; the base ground of the tunnel should be carefully treated, otherwise floor mudding may occur during the operation of the tunnel.