Abstract: Laboratory incubation experiments were conducted to compare the inhibitory effects of dicyandiamide (DCD) and 3,5-dimethylpyrazole (DMP) on nitrification in meadowcinnamon soil and fluvo-aquic soil, the main soil types of North China Plain. The synergistic effect of DMP combined with urease inhibitor hydroquinone (HQ) on nitrogen transformation in fluvo-aquic soil was further studied. The results indicated that, in contrast to DCD, DMP had a stronger inhibitory effect on the nitrification in the two tested soils. In comparison with the treatment without any inhibitor, the soil NH₄⁺-N content in the treatment with DMP increased significantly by 149.5%-387.2% at the peak of nitrogen transformation stage, and the soil NO₃^--N content reduced by 22.3%-55.3%. The inhibitory effects of DCD and DMP in fluvo-aquic soil were both stronger than in meadow-cinnamon soil. In addition, the application of DMP combined with HQ had a significantly synergistic effect on soil nitrogen transformation.