The construction sector in China is a significant contributor to the nation's energy consumption, representing approximately 30% of the total energy usage, and this proportion is increasing year by year, making the construction sector gradually become the primary area of energy consumption. In regions with hot summers and cold winters, passive residential buildings face a difficult dilemma between energy conservation and providing a comfortable living environment. This study is dedicated to optimizing the design of the enclosure structure of residential buildings in hot-summer and cold-winter regions. By using SketchUp and Energy Plus software for modelling and analysis, the study deeply explores the impact of the heat transfer coefficients of external walls and roofs on the heating, cooling load, and the total annual load of the building, aiming to find the best design scheme for the enclosure structure. In terms of material selection, this study chooses polyurethane insulation panels as the insulation material for external walls, with an insulation layer thickness set at 130 mm; for the roof insulation, extruded polystyrene boards are used, with an insulation layer thickness of 160 mm, which can achieve the lowest total annual load. The results of this study provide a theoretical foundation and practical guidance for the design of the enclosure structure of low-energy buildings in regions with hot summers and cold winters.