Abstract: This paper is about the Zhengzhou-Xi'an high-speed railway, in particular, the Tongguan section about their potential seismic subsidence. A large number of undisturbed loess samples were collected at Tongguan section. By inputting artificial synthetic seismic wave to the dynamic triaxial testing of the samples, the seismic subsidence experiments were carried out. Based the laboratory tests, the paper obtains the following results. Firstly, the seismic subsidence of loess foundation was estimated and the foundation dynamic numerical model was established. Secondly, It further examined the permanent deformation of the sub-grade loess at the levels of 10% and 2% exceedance probability in 50 years under the earthquake effect and the sub-grade loess after soil treatment. The results showed that, the settlement occurred mainly in Q3 loess. The foundation treatment measures such as dynamic compaction, down-hole dynamic consolidation can effectively reduce the settlement of the loess foundation. However, larger settlement can still be generated under strong earthquakes if the soil treatment depth is not deep enough. The results presented in the paper can provide a basis for the foundation seismic treatment.