Hulun Lake, as a typical representative of inland lakes in the cold and arid areas of northern China, plays an irreplaceable role in water conservation, climate regulation, windbreak, and sand fixation. This lake maintains balance in the Hulun Buir grassland ecosystem and even the ecological-security barrier of northern China. Thus, identifying the main ecological-security problems in Hulun Lake Basin and improving its ecological-security evaluation index system are highly significant. The obtained data can be used for the scientific research and assessment of the ecological environment status of Hulun Lake, the maintenance of regional sustainable development, and the accurate implementation of bottom-line management and control policy.Based on remote-sensing imagery, ground survey, experimental simulation, and other multi-scale data analyses, this paper aims to analyze and identify the ecological-security problems of Hulun Lake area and their causes by combining historical data collection, expert consultation, and department interview. The results are as follows:(1) warm and dry climate, overgrazing, and other factors induce significant grassland degeneration, so land desertification and salinization area expand. (2) grassland degradation increases water-pollution load, such as hay into lake, atmospheric dry and wet settlement, and soil erosion. (3) climate warming and drying cause wetland shrinkage. Long-term overfishing and other human activities lead to the depletion of fishery resources and significant fish miniaturization. Consequently, the stability of aquatic ecosystem is reduced, and blue-green algal blooms occur frequently. Based on the comprehensive diagnosis and analysis of regional ecological-security problems, together with theoretical guidance by the methodology of mountains, rivers, forests, fields, lakes, and grass-system methodology, and improving the ecological environment quality of Hulun Lake basin as the core goal, the pressure-state-response (PSR) model is adopted in the present study according to the principles of focalization, scientific nature, operability, and systematicness of evaluation indices. The pressure subsystem comprises five first-class indicators, namely, meteorological conditions, population, water resources, water environment pressure, and human activities. The state subsystem comprises six indicators, namely, water environment, water ecology, land ecosystem, ecosystem service function and sensitivity, landscape pattern, and ecological risk. The response subsystem comprises two indicators, namely, ecological-management measures and ecological-management investment. Then, they jointly form an ecological-security evaluation index system with the integration of sky and land and the overall planning of land and lake, which includes 13 first-class indicators and 38 second-class indicators, to serve as a reference for studying the ecological-security evaluation of Hulun Lake and similar lakes in cold and arid areas.