Abstract: The thermal environment inside solar plastic greenhouses with oneslope is very important and complex. Considering almost all factors that are evident, a thoretical model was set up to discribe the thermal environment, and was verified through experiments. The simulation results showed that the air temperature inside is mainly affected by the outside solar radiation, and the air temperature outside has only a secondary effect. The back wall of greenhouse plays an important role in maintaining the inner thermal condition, which is steadily improved with the improvement of greenhouse thermal insulation and especially with the use of transmittinginsulating material.