The CFD (computational fluid dynamics) simulation technique has been utilized based on the experimental observation data of solar greenhouse in Jinan. The humidity distribution in the observed solar greenhouses under natural ventilation is simulated based on the standard κ-ε turbulence model and the DO (discrete ordinates) radiation model. The results are as follows. 1) The CFD numerical technique can perform a satisfactory simulation of the humidity variation in solar greenhouse under natural ventilation. The average error between the simulated and observed humidity is 5.5%. 2) The humidity in greenhouse shows a distinguished vertical distribution (high humidity in the lower layer and lower humidity in the upper layer) due to weak dehumidifying ability of natural ventilation under low wind speed condition; the dehumidifying effect obviously improves with wind speed increasing and the humidity presents a distribution of higher level in the northern part and lower level in the southern part. 3) The wind direction is the major dynamic factor regarding the greenhouse ventilation and has a strong impact on dehumidification. When it is easterly wind in the same direction with the greenhouse, the humidity is low and distributed evenly in the greenhouse with higher dehumidification efficiency. When it is north wind, the humidity has significant spatial difference and leads to lower dehumidification efficiency. This analysis can be a scientific reference for structural optimization and environment management of solar greenhouse.