Abstract: Aiming at computing the heat transfer through multi-layer covering in environmental control design and insulation performance evaluation of a greenhouse, a computing method for thermal transmittance of multi-layer covering was developed based on the data of a single screen. According to heat transfer theory, the formula for saving ratio of heat loss of multi-layer screens were established from that of a single screen, and then the method for calculating the thermal transmittance of multi-layer covering was developed. The computing formula which quantifies the relationship between the heat transfer parameters of multi-layer covering and a single screen become simple by using a new parameter—heat insulation ratio. The high accuracy of the computing formula has been synthetically texted by different kinds of data. In a same case, the saving ratio of heat loss of three-layer screens established from that of a single screen was only 4.6% different from the same saving ratio of heat loss. The computing method developed in this paper can be used to calculate the saving ratio of heat loss and thermal transmittance for multi-layer covering, and avoid measuring the parameters of different multi-layer covering consisting of kinds of materials seriatim.