The heat transfer coefficients of two foam glass exterior thermal insulation walls were tested by weather-resistant testing instrument and heat flow meter. The experimental values were compared with the theoretical values. The results show that with the temperature differences Δt>20 °C, the testing errors of two walls are smaller than 1% and 3% respectively. In view of thermal performance, testing accuracy and operability, the test program is practicable to meet the testing requirement with a temperature difference greater than 20 °C and without seasonal restrictions. In the zones without heating such as hot summer and cold winter zone, therefore, the weather-resistant testing instrument (i.e. temperature control box) and heat flow meter can be used to test the heat transfer coefficient of a wall.