The paper aims to introduce the relevant indicators, testing methods， and application steps for testing and evaluating the thermal performance of external windows, and analyze how to test and evaluate the thermal performance of external windows based on practical cases. The thermal performance of external windows is comprehensively evaluated through various methods such as heat transfer coefficient test, solar radiation coefficient test, window frame linear heat transfer coefficient test, air tightness test and optical performance test, so as to provide scientific basis for green building design and building energy efficiency improvement. Practical case studies have shown that adopting appropriate testing methods and evaluation indicators can effectively improve the energy efficiency and comfort of buildings， making contributions to sustainable development.