The improving effects of Platycladus orientalis,Robinia pseudoacacia and the two mixed plantations on soil fertility on the Loess Plateau were investigated.In the Loess Plateau area,planting plantation had much help for the improvement of the nutritional element content,such as soil organic matter,total nitrogen,total phosphorus,available nitrogen and quick-acting potassium,and different plantations had different enhancement degrees.Except total potassium and quick-acting phosphorus,every target in nitrogen fixation plantation was higher than that in non-nitrogen fixation plantation.In general,the enhancement of soil fertility in nitrogen fixation plantation is more remarkable than that in non-nitrogen fixation plantation.