A single-slope greenhouse (SSG) is the general name of a kind of agricultural greenhouse facility widely used in China. Microclimate studies for SSGs in Weifang, Shandong Province, are relatively scarce. This paper mainly discusses the test data of nine SSGs including temperature, humidity, solar global radiation intensity, CO2 concentration, wind speed, and vapor pressure deficit (VPD) trend. Moreover, the conservation of quality method is used to estimate the ventilation volume and humidity growth after opening the top vent in the greenhouse. Through the analysis in this paper, for local SSGs, the internal environmental change has commonality but its internal environment is still influenced by many factors, such as plant planting density, internal cover, plant growth height, and vent opening time. In addition, the method in this paper can provide a quantitative tool for calculating and controlling humidity for researchers and greenhouse workers and provide a basis for greenhouse ventilation strategies.