Systematic conservation of earthen sites encompasses two fundamental dimensions: the scientific comprehension of the site system and the systematic implementation of conservation measures. Through an in-depth analysis of the historical development and current challenges in the conservation of earthen heritage sites in China, this study builds on the synthesis of historical, theoretical, and practical experiences. By applying system theory, a value-centric framework is established to define the earthen site system through its conceptual components, structure, functions, state parameters, and phase states, while clarifying system boundaries and environmental interactions. The scientific essence of conservation is identified as preventing or mitigating the transition of earthen site systems from their current non-uniform ordered state to a uniform disordered state. Here, the system's state reflects the preservation status of heritage values and informational integrity, with deterioration acting as the state variable. The assessment of an earthen heritage system's state essentially evaluates the actual or potential impacts of deterioration on the long-term preservation of the system's heritage values. The conservation measures subsystem integrates management, preventive measures, intervention techniques, and utilization strategies. Utilizing synergetics, this study reveals the coordination mechanism among these measures and proposes effectiveness as the order parameter governing the subsystem. Quantitative characterization of the subsystem's state is achieved through conservation effectiveness metrics. The synergistic interaction of these four categories of measures constitutes a holistic systematic conservation approach.