Abstract: According to the hot box method, the test apparatus measuring the overall heat transfer coefficient of greenhouse covering materials was developed. And it is the special equipment that adapts to heat transfer ways and working environment characteristics of the greenhouse covering materials. By adjusting control devices, such as cooling device, heating device, ventilating device, commutating device, dehumidifying devices and so on, this test apparatus so comprehensively and stably simulates and realizes working conditions that are close to real working conditions of the greenhouse covering materials, including internal and external air temperatures in greenhouse, wind speed, sky radiation temperature, etc. Even it really shows that every factor has an effect on the overall heat transfer of the covering materials. Its measuring conditions are easily adjusted and measured values are exact under condition.