In this study, 3-4 stand plots of 20 m×20 m to 30 m×30 m were selected from four typical forests located in a small watershed of Xiangshui River, the Liupan Mountain of Ningxia, China, to explore the spatial variability of inorganic nitrogen (NH₄⁺-N, NO₃^--N) fluxes and their relationships with precipitation. The concentration and flux of the inorganic nitrogen (NH₄⁺-N, NO₃^--N) in the infiltration water penetrating the soil of main root layers (0-30 cm) after precipitation, the water penetrating tree canopies (that is, canopy infiltration water), run-off water and the water infiltrating humus layers (that is, humus infiltration water) were measured during the growing season (24 of May to 20 of October) of 2011. The results showed that with the atmospheric precipitation of 724.3 mm in the open field, the concentration (kg/hm²) of inorganic nitrogen (NH₄⁺-N) in canopy infiltration water was 2.40 for the plantation of Larix principis-rupprechtii, 2.37 for the secondary forest of Pinus armandii, 2.29 for the bush of Prunus salicina, and 2.09 for the secondary forest of Betula platyphylla, respectively, and they all were lower than that in the rainfall of the open field, 3.04. The corresponding NO₃^--N fluxes (kg/hm²) were 2.15 for the plantation of Larix principis-rupprechtii, 2.14 for the secondary forest of Betula platyphylla, 2.09 for the bush of Prunus salicina, and 1.92 for the secondary forest of Pinus armandii, respectively, and also much lower than that in the rainfall of the open field, 4.27. Overall, the canopy adsorption effect of inorganic nitrogen was greater in the broad-leaved forests than in the coniferous forests. Among the four forest types, the humus infiltration water had an inorganic nitrogen concentration range of 0.68-0.88 mg/L, which was slightly higher than those in the canopy infiltration water. The inorganic nitrogen fluxes in the humus infiltration water were 4.10 for the bush of Prunus salicina, 3.24 for the secondary forest of Betula platyphylla, 3.22 for the secondary forest of Pinus armandii, and 2.77 for the Larix principis-rupprechtii plantation, respectively, and lower than those in the canopy infiltration water. In both the secondary forest of Pinus armandii and the plantation of Larix principis-rupprechtii, the concentrations of inorganic nitrogen in the soil infiltration water of the main root layer (0-30 cm) were higher than those in the humus infiltration water. Due to the soil leaching effect, the inorganic nitrogen flux carried by the soil infiltration water of the main root layer was 16.34 kg/hm² for the stand of Pinus armandii and 18.93 kg/hm² for the stand of Larix principis-rupprechtii, being obviously much higher than those in the humus infiltration water. In summary, precipitation plays an important role in the inorganic nitrogen fluxes input into the forest soils, and the absorption or up-taking effects of tree canopies and humus layers greatly reduce the amount of the inorganic nitrogen flux into soils through precipitation. However, the soil leaching effect in the main root layers can markedly increase the inorganic nitrogen flux of the soil infiltration water, indicating the loss of the inorganic nitrogens in the forest ecosystems.