Abstract: The steady-state thermal transmittance of a multiple glazing with structure of 6 mm ordinary transparent glass/12 mm air layer/ 6 mm ordinary transparent glass was determinated by guarded hot plate method with CD-8080 type double sample coefficient of thermal conductivity detector according to GB/T 22476-2008 “Calculation and Determination of Steady-state U Values(Thermal Transmittance) of Multiple Glazing”, and the uncertainty of the test results was analyzed and evaluated according to JJF 1059-1999. The results show that the steady-state thermal transmittance of the multiple glazing was U=(2.8±0.2) W·m-2·K-1 and the coverage factor k=2. Uncertainty from the determination average heat flow of the heating measurement unit was the uppermost factor affecting the test results of the steady-state thermal transmittance of the multiple glazing, uncertainty from the temperature measuring was the minor factor, and uncertainty from the rounding off of numberical values was the least factor.