The air tightness of 5 different types of common used windows in Tianjin University were measured by blower window method; the measured windows including PVC single, PVC double, aluminum alloy casement, aluminum alloy sash and aluminum alloy slanting sash windows. We totally measured 15 windows with every type 3 windows. The pressure difference between window and outdoor air was controlled in 0~60 Pa during every test. According to the measured results, we compared the influence of window frame material, opening form, function time and outdoor environment on the performance of air tightness. With 5 Pa pressure differences, the infiltration rate of aluminum alloy slanting sash windows was 35~40 m³/h, others were 10~20 m³/h. The window air tightness had a great effect on window leakage coefficient C but less effect on pressure coefficient n, and the coefficient n of all the 15 windows was 0.5-0.6. The air tightness of the 15 windows was calculated through GB/T 7106-2008, the PVC double windows were the tightest with an infiltration rate of 5.17 m³/h·m², while the aluminum alloy slanting sash windows were worst and its infiltration rate was 17.9m³/h·m². Based on the results of 3 repeatability tests, we found the outdoor climate influence was negligible on the test results when the pressure difference was larger than 15 Pa. The time interval was one week for every repeatability test, most of the test error was less than 15% between every two tests.