Abstract: The low-altitude economy has been elevated to a national strategic emerging industry and constitutes a vital component of new quality productive forces, with its market size exhibiting sustained, rapid growth. Nevertheless, the rapid industrial expansion has been accompanied by frequent safety incidents such as unauthorized drone flights, illegal airspace intrusions, and illegal aerial deliveries. Compounded by the inherent detection difficulties of low-slow-small targets, severe terrain occlusion and electromagnetic interference in urban environments, and inconsistent security standards across different controlled zones, the conventional security solution relying solely on independent radars and optoelectronic detectors suffers from pervasive drawbacks including extensive detection blind zones, insufficient recognition accuracy, poor data interoperability, and slow emergency response, making all-domain integrated prevention and control unachievable. Against this backdrop, this paper takes the 5G-A integrated communication-sensing-computing-intelligence technology as the core support, thoroughly analyzes three core challenges confronting low-altitude security: target characteristics, environmental interference, and diversified application scenarios, and elaborates on the fundamental principles and strengths of key technologies including integrated communication and sensing as well as multi-source heterogeneous data fusion. A four-tier overall architecture for low-altitude security is constructed, consisting of the perception layer, network layer, platform layer, and application layer. This architecture integrates diversified devices such as 5G-A ISAC base stations, low-altitude radars, optoelectronic detectors, radio frequency spectrum detection systems, and Remote ID. Supported by artificial intelligence models, the system realizes accurate capture, classification, and risk assessment of low-altitude targets. The proposed system has been deployed and verified in typical scenarios including civil aviation airports, border ports, major large-scale events, and mountain scenic spots. Field test data demonstrate that the positioning error of the system is less than 10 meters, the target recognition accuracy exceeds 95%, and both the false alarm rate and missing detection rate are below 5%. The efficiency of emergency disposal is greatly improved, effectively addressing the long-standing industry pain points of low-altitude security: “invisible targets, disconnected devices, and ungovernable airspace.” The technical scheme and practical deployment paradigm proposed in this paper can serve as a reference for the construction of nationwide low-altitude security systems. Looking ahead, with the evolution from 5G-A to 6G and the in-depth application of large AI models, low-altitude security will gradually enter a new phase featuring intelligent prediction and proactive prevention and control, continuously safeguarding the safe, efficient, and large-scale development of the low-altitude economy.