Windows are the weakest component of a building’s thermal performance. While existing optimizations have significantly improved the heat transfer coefficient (U-value) and solar heat gain coefficient (SHGC) of windows, most of these technologies are only suitable for a single season. The adoption of adjustable wall-like windows has emerged as one of the most effective strategies to address this issue. In this work, a novel adjustable wall-like window (WLW) is designed to balance insulation and shading effects, based on the requirements for summer shading, winter insulation, and the construction forms of composite windows. It consists of a double-glazed window filled with argon gas and a layer of aerogel board. Experimental testing and numerical simulations are conducted to analyze the heat transfer process of the wall-like window. Additionally, the effects of cavity thickness (D1), aerogel thickness (D2), and surface emissivity (ε) on its optical and thermal performance are investigated. The results indicate that when the cavity thickness (D1) is less than 20 mm, heat conduction dominates within the cavity, significantly affecting the U-value of the wall-like window, while its influence on the SHGC is relatively minor. The aerogel thickness (D2) shows a nonlinear inverse relationship with the U-value. As the surface emissivity (ε) increases, both the U-value and SHGC of the wall-like window rise. However, ε has a more pronounced effect on the U-value than on SHGC. The visible transmittance declines steadily with aerogel thickness but is unaffected by D1 and ε. In cold regions, the proposed adjustable wall-like window can further reduce energy consumption beyond the baseline of ultra-low energy public buildings, with an energy-saving rate of approximately 13%.