A new method was designed for direct determination of ¹⁵N abundance of NH₄⁺, NO₃^- and NO₂^- in soils with mass spectrometry. The principle of this method was based on analysis and quantification of ¹⁵N abundance of the N₂O produced from NH₄⁺,NO₃^-and NO₂^- through transformation reactions catalyzed with their respective specific chemical reagents separately. The measured values of ¹⁵N abundance of the N₂O tally well with their respective reference values in NH₄⁺, NO₃^- and NO₂^-. The method was characterized by quickness, simpleness and freedom from contamination of atmospheric nitrogen. Especially this method has a very low detection limit, and 5～20 μg N in the sample is adequate for detection. Therefore, it will be of a great help to study on mineralization, nitrification and denitrification of nitrogen in soils.