Abstract: In order to clarify how the physical properties of an outer-shading screen effect the solar radiation environment inside a greenhouse, a study, based on heat radiation theory, was undertaken. After making a detailed analysis of the transfer pathways of solar radiation inside the greenhouse, a model was developed for the multi-span plastic greenhouse equipped with outer shading screens. The experiment, which was conducted in a small-scale greenhouse, showed that when using different screen materials with the same transmittance but different reflectance, a greenhouse shaded with higher reflectance material has better illumination inside. The measured results are in close agreement with the simulated results.