In this paper, a numerical model is presented for simulating the variations of temperature (including soil temperature) and humidity within an artificial forest. The theory is based on the turbulence equations of thermal-dynamics in meteorology. The main factors we consider in present model are: the radiation of the sun and thermal processes within a forest canopy, the evapotranspiration of the tree, the geometric feature of the canopy, and the physiologic properties of leaves etc., which are not considered by meteorologists in their routine works.As we compare the results from the model with the observation data, the consistency is quite satisfactory.