Abstract: The research shows that soil urease activities are significantly correlated to the nutrition content,which can be used as the biological index to evaluate the soil fertility.Urease activity decreases gradually as soil becomes deep;soil urease activity amount increases as crop grows and root amount strengthens,which is significantly correlative to the amount of soil microbe.Soil urease activity of rhizosphere is higher than that of non-rhizosphere;soil urease activity of rhizosphere is apparently different in different kinds of Leguminosae herbage.Leguminosae herbage with deep roots such as alfalfa and sweet clover,leaves the deep soil plenty of root residue,which helps to improve the urease activity and soil fertilily of deep soil.