In response to the national “14th Five-Year Plan” to vigorously promote prefabricated construction and enhance the energy efficiency of new buildings and to contribute to the achievement of the nation's “dual carbon” target, a prefabricated structural insulation integrated composite sandwich wall panel is proposed. To achieve a fully dry connection for these wall panels, solid concrete frames are positioned around the perimeter of the panels as one of the connectors. The presence of concrete frames creates a significant thermal bridge, which largely determines the thermal performance of the wall panel. Quantifying the effect of the frame ratio on the thermal performance of the wall panel is of great guiding significance for its structural design optimization and practical engineering application. Therefore, six sets of wall panel specimens with varying frame ratios were designed and tested by calibrated hot box method in this study to quantitatively analyze the effect of the frame ratio on the thermal performance of prefabricated wall panels. The experimental results reveal that the presence of concrete frames not only postpones the time to reach a steady state in thermal transmission but significantly reduces the thermal performance of the wall panel. When the frame ratio is 19.94%, 30.85%, 40.95%, 50.26%, and 61.43%, the thermal resistance of the wall panel is reduced by 79.26%, 84.28%, 87.48%, 89.36%, and 91.10%, respectively. To meet the current building energy-saving requirements, the frame ratio of the wall panel should be controlled within 20% in practical engineering applications. Through a comparative analysis of various methods for calculating wall panel thermal resistance with experimental results, it is recommended to use the zone method as the thermal resistance calculation method for wall panels with concrete frames.