Abstract: With the desert steppe of Inner Mongolia Plateau as research object, in which the Stipa breviflora Griseb., A rtemisiafrigida Willd. and Cleistogenes mutica Keng were major plants, the tests of warming facilities and nitrogen application were conducted under natural field conditions to study the change laws of soil organic matter in each soil layer and with different treatments under the conditions of fertilization and warming, fertilization without warming, warming without fertilization and neither fertilization and warming. The results showed that the organic matter contents in soil were all increased under the warming and nitrogen application conditions and that were all reduced gradually with deepening of the soil under 4 treatment conditions. Under the action of warming and nitrogen application, the organic matter content in soil in 2008 was evidently lower than that in 2007, which had great relation to rainwater in those years. The change taws for the organic matter contents in different depth of soil in control area were consistent, which all diminished gradually with year increasing.