The Great Wall of the Ming Dynasty starts from the Hushan in eastern China's Liaoning Province, to the Jiayuguan in western China's Gansu Province, totalling 8851.8 km in length. The Great Wall is a precious historical and cultural heritage in China. It was listed as a world heritage site by UNESCO in 1987. The Chinese government has always attached great importance to the protection of the Great Wall and has taken a lot of effective measures. However, because of the ages and economic and social development, the Great Wall is still facing quite serious human threats and natural destructions. Therefore, it has become the consensus of the Chinese government and all the researchers to further strengthen the protection of this precious cultural heritage of mankind, which is of outstanding and universal value throughout the world. Based on field investigation and sampling in Yongning of the Great Wall of the Ming Dynasty, basic physical and mechanical properties and SEM experiment of the Great Wall soil were carried out, and the main mineral composition, chemical composition, and microstructure characteristics of rammed soil of the Great Wall were obtained. According to the natural environment conditions of the Great Wall, a one-way freeze-thaw cycle device was developed to study the migration law and microscopic mechanism of water and salt of rammed soil. The results provide scientific data for the long-term preservation, display and utilization of the Great Wall site.