It needs a long complex process to establish an artificial froest ecosystem in the fragile natural environment with serious soil and water loss in loess hilly area, Because the artificial forest should be steady and productive within a very shorter period than that of natural forest needs, we should study the ecological relationship of natural system.The system we built should have as less as possible of resistant and competitation in it, so that the system could be efficient.Therefore the structure and function of those artificial system is the key in their erecting process.We had made a wrong step in land harnessing and afforesting for our overlooking to the natural law.