<p>With the proposed goals of “energy conservation, carbon reduction, and green development,” green and low-carbon lifestyles have gained significant attention. As a major sector of energy consumption, residential buildings face common issues such as high energy consumption, poor comfort, and aging facilities. Taking a residential building in the West Coast New Area of Qingdao, Shandong Province as a case study, this research employs field surveys and DesignBuilder software simulations to analyze the performance of building envelopes and interior walls in non-heated spaces. The thermal insulation performance differences are compared across three stages: the original building, preliminary retrofit, and passive ultra-low energy stage. On this basis, a parametric analysis of the thermal performance of passive ultra-low energy building envelope components was conducted. The results demonstrate that passive ultra-low energy retrofitting of the building envelope can achieve an energy-saving rate of up to 87.06% compared to the original building, and 84.9% compared to the preliminary retrofit. This research, focusing on the parametric analysis of passive ultra-low energy envelope performance in existing residential buildings, provides a theoretical foundation for energy conservation and carbon reduction in existing residential buildings.</p>