The aim of this study was to analyse the number of test reports issued and the characteristics of U-values, for 15,396 window-system efficiency test reports on the web-site of the Korea Energy Agency, are as follows, The annual U-values continued to improve as the consumption efficiency rating was strengthened, showing a median of 0.895W/(㎡·K) in 2021, 0.9 or less based on the first grade, and it was confirmed that the proportion of new testing laboratories were large and 50% of the report issued. As a result of checking the data characteristics of U-values between testing laboratories, the existing testing laboratory was 1.126W/(㎡·K), the new was 0.897W/(㎡·K), and the in-house was 1.190W/(㎡·K).