Xi'an City Wall is one of the largest and most complete ancient cities in China, with a total length of 13.74 kilometers. Today, it has shown a good trend in protection and tourism development: architectural structure and preservation situation • Ontology status: the main body of the city wall is still relatively complete after years. However, there are inevitable problems with some diseases, such as the settlement, cracks, displacements of the wall, and the internal hollow and loose bodies. However, through the comprehensive "medical examination" of the city wall from 2020-2021, the overall preservation status has been clarified and a detailed "health file" has been established. • Architectural characteristics: The scale and style of the expansion after the Ming Dynasty are retained, including the city gate, the city building, the arrow building, the corner building and other buildings, including the light gate also retains the relics of the city gate south of Tang Chang'an Emperor City. Protection measures and scientific and technological applications • Monitoring system: relying on the intelligent guardian of "digital sentry", with more than 3,000 monitoring points and more than 1,300 intelligent terminals, can capture core data everywhere in the city wall in real time, and realize all-round visual control of the hidden dangers of the city wall structure. "Digital cabin comprehensive management platform" can monitor the "health status" of each point of the wall through the "green yellow orange red" four-color warning, and the system will immediately issue an alarm when the monitoring data touches the preset cordon. • Protection mode: A unique "preventive protection mode" has been formed, from disease "medical examination" to technology empowerment monitoring, to the integration of traditional processes and modern wisdom, to inject new vitality into the ancient city walls. For example, the city wall drainage system was successfully remodeled in 2021 to effectively prevent rainwater erosion; In 2023, the city wall was "full-body CT scan" through advanced survey methods, providing important data for internal structure protection. Tourism development and supporting services • Tourism facilities: Since the whole line was connected in 2005, bicycle rental services have been provided to tourists, and they can ride around the city for a week. There are also entertainment facilities such as VR experience area on the city wall. • Tourism popularity: As an important tourist attraction in Xi'an, it attracts many tourists to visit and visit, carrying city memories and cultural feelings, and is an important window to feel the charm of the ancient city.