Abstract: By analysing argillic and water characteristics of clay pan,this paper presented the following three factors by which the growth of forests was influenced.1).The soil was extremely compact with very few big pores and many small pores in the soil.This made the roots very difficult to penetrate lower soil layer.2).The clay pan kept superfluous water on the surface because of its little water capacity.As a result,this frequently made the soil in reduction,and caused a high concentration of Fe and Mn which might be toxic to the plants.3).As non-effective water content was high while effective water content was low in clay pan,the forest trees suffered from a physiological drought.Besides,this paper presented some proposals for improving the soil as well.