Abstract: With laboratory incubation method at constant temperature under aerated conditions, the effects of 4 fumigants Chloropicrin (Pic), methyl iodide (MeI), 1,3-dichloropropene (1,3-D) and methyl disulfide (DMDS) on soil N mineralization and nitrification under vegetable greenhouse conditions in Beijing area were studied. The results reveal that mineral N concentration increases significantly in a short-term period after fumigant treatment. Cumulative N mineralization under 1,3-D, MeI, DMDS and Pic treatments are 320.62 mg·kg^-1, 317.25 mg·kg^-1, 287.87 mg·kg^-1 and 278.73 mg·kg^-1 respectively. This represents corresponding increases of 68.85%, 67.07%, 51.60% and 46.78% compared with untreated soils (189.89 mg·kg^-1). Fumigation strongly inhibits nitrification. Compared with the control, ammonium nitrogen content increases after fumigation. MeI treatment has the highest ammonium nitrogen (194.97 mg·kg^-1) and control treatment has the lowest (28.82 mg·kg^-1). Nitrification inhibition rates by Pic, 1,3-D, DMDS, MeI treatments are 40.8%, 20.8%, 26.9% and 24.1% respectively. Nitrification is inhibited for at least 2 weeks after treatment with Pic, 1,3-D and MeI, and at least for 1 week after treatment with DMDS. Nitrification and mineralization gradually recover under long-term incubation.