Abstract: An experiment was conducted to study the effect of immature loess subsoil fertilization in current year on productivity and rhizospheric soil nutrient and biological activity of cereal crops. The results show that fertilization promotes crop root growth and productivity. A strong root-soil system in turn promotes the multiplication of microbes, enzyme activity, and increases soil nutrient. Aging of immature loess subsoil should adopt measures of both utility and maintenance, with emphasis on soil biological conditions. The study indicates that sorghum and maize could be planted as the pioneer crops to improve immature subsoil conditions. Sorghum owns strong and deep root system, and great biomass. Although the root weight, maximum root length, and number of adventitious root are not as high as those of sorghum, microbe amount and enzyme activity in rhizospheric soil of maize are high enough. Compared with sorghum and maize, broomcorn is not suitable for the improvement of immature subsoil due to its weak root system and low biological activity in rhizospheric soil. Immature losses subsoil is sensitive to fertilization. Since fertilization of immature loess subsoil is achievable with high annual yields, it serves as a significant aging factor of immature subsoil. Aging of immature loess subsoil is both an input and transformation process of matter and energy among plants, soils, microorganisms, including fertilization, crop production, resolving and mineralization of soil microbes, and catalysis of soil enzymes.