Samples of subtropical acidic forest soil werecollected for incubation in an in-lab microcosm chamber. Some of the samples wereamended with organic carbon or organic nitrogen. Then the incubated soil samples were analyzed for soil nitrification activity and abundance of functional genes of bacteria AOB and archaea AOA, and further for rules of extraneous organic carbon and organic nitrogen affecting ammonia oxidation in the soil. Results show that the amendment of extraneous organic nitrogen stimulated significantly soil nitrification activity.Acetylene inhibition tests demonstrate that autotrophic ammoxidation explained over 90% of the soil nitrification in the subtropical acidic forest soil. The addition of organic carbon did not have much effect on nitrification activity, nor did the amendment of organic carbon and inorganic ammonium simultaneously. However, the addition of organic nitrogen enhanced soil N mineralization, thus causing soil ammonia contentto increase, which may probably be the main cause of the significant increases in soil nitrification activity and abundance of AOA and AOB.