The tertiary formation in the Tianshui Basin is classified as Western Qinling, Gansu group. The Liangjiashan tunnel travels through the tertiary mudstone in the Tianshui Basin. In order to determine the geological properties of surrounding rock, the tests for geochemistry and mineral composition of mudstone specimen have been conducted. The test results from the Liangjiashan Tunnel were compared and correlated with the results from Xiashan section. It was indicated that the test results from the two sites correlate each other very well and can characterize the geological characteristics such as formation, tectonic background and its evolution of the mudstone in the Liangjiashan Tunnel. This can provide basic evidence for the studies on the compositions, weathering characteristics, sedimentary environment and tectonic background of the Tianshui Basin. This research can also be considered as a good example and supply the fundamental data for studies on related geological problems by using tunnel construction.