Low-altitude surveillance serves as a crucial safeguard for the safety of low-altitude operations, ensuring the secure and efficient functioning of aircraft in low-altitude airspace. Compared with high-altitude systems, advances in low-altitude aviation are presenting a new landscape characterized by high density, autonomy, and heterogeneity. To establish a low-altitude surveillance technology system with no blind spots, a model-based systems engineering (MBSE) approach is introduced into the design process of low-altitude surveillance systems. Based on the MagicGrid system modeling framework, a model-based design methodology and process are proposed. This includes defining stakeholder requirements, formulating operational schemes for low-altitude surveillance missions, conducting functional and physical decomposition, and performing engineering analyses of performance parameters. The low-altitude spectrum monitoring and positioning system is used as an illustrative example. The requirements, structure, behavior, and parameters of the low-altitude surveillance mission are modeled using SysML. It is concluded that MBSE can enhance the consistency and traceability of design information through system models, providing a valuable reference for the application of MBSE methods in the design of low-altitude surveillance systems