To evaluate the effects of decreased precipitation on soil N cycle, we investigated monthly dynamics of soil inorganic nitrogen (SIN), nitrogen mineralization rate and leaching in three precipitation treatments (ambient, precipitation reduce by 30% and 50%) under Mongolian pine plantation in the Horqin Sandy Land. Our results showed that soil nitrate was main form of SIN pool in Mongolian pine (Pinus sylvestris var. Mongolica) plantation, and stimulating precipitation reduce could lead to the declines of soil nitrate concentration (P < 0.05) and nitrate/SIN ratio (P < 0.001), but increase of soil ammonium concentration (P < 0.05). Soil net nitrification rate and net mineralization rate decreased in precipitation reduce treatments compared with ambient precipitation (P=0.002), but there were no differences of soil net ammonification rate among three treatments (P=0.86). Soil inorganic N was mainly leached through soil nitrate in Mongolian pine plantation, and precipitation could significantly reduce soil ammonium leaching (P=0.04), but there was no difference of soil nitrate leaching (P=0.09). In addition, soil inorganic N concentration, net N mineralization rate and leaching had monthly dynamic characteristics, consistent with the monthly dynamic of precipitation in the Horqin Sandly Land. There were significant interactions between precipitation treatment and sampling time on SIN concentration and soil net nitrogen mineralization rate, but not for soil inorganic N leaching. Our study implies that the change of precipitation can alter soil N availability, mineralization rate and leaching, and in future precipitation reduce may decrease soil nitrogen availability under Mongolian pine plantation in the Horqin Sandy Land.