Abstract: Tongwan City, which is located in Jingbian, Yulin, Shaanxi Province, is the only Xiongnu city site in China, carrying rich historical culture and scientific value. Despite over 1,600 years of weathering and freeze-thaw cycles, the heritage site has been preserved to this day. Therefore, it is important to study the material composition, mechanical properties and microstructure of the site soil for the restoration of heritage site. Taking the site soil at Tongwan City as the research object, this study conducted laboratory tests on physical and mechanical properties, X-ray diffraction(XRD), X-ray fluorescence(XRF) spectroscopy, scanning electron microscope (SEM) and computed tomography (CT) scanning to analyze the macro and micro characteristics of the site soil. Based on the above research, some conclusions are as follows. ① The primary mineral components of the site soil include quartz, feldspar, calcite and dolomite, and its calcium ion content is significantly higher than the surrounding soil samples, this indicates that lime material was intentionally added during the construction of Tongwan City. ② Compared with undisturbed loess in the surrounding area, the site soil has higher shear strength and low compressibility, the shear curve exhibits distinct brittle failure deformation characteristics, and the compression coefficient is smaller. ③ Microstructural analysis reveal that face-to-face contacts dominate the particle interactions in the site soil. Calcium carbonate cement interweaves densely among particles, adhering to particle surfaces and bridging interparticle spaces, which reduces the proportion of macropores, enhances particle interconnections, and increases the overall density of the soil structure.