An in-situ field experiment was established to examine the effects of increased precipitation and nitrogen deposition on the activities of soil enzymes in the semi-arid Leymus chinensis grassland of inner Mongolia during the 2014 growing season. Water was added at two levels (W0, no additional water; and W15, a 15% surplus on average rainfall) and N was added at four levels (CK, 0 kg N hm^-2a^-1; LN, 25 kg N hm^-2a^-1; MN, 50 kg N hm^-2a^-1; and HN, 100 kg N hm^-2a^-1) to simulate increasing precipitation and N deposition in a future global change scenario. Effects of different water and nitrogen additions on the monthly dynamics of N cycle-related protease, urease, nitrate reductase, and nitrite reductase activities in grass topsoil were quantified. We also analyzed the correlations between all variables and soil physical and chemical properties. Results showed that, under natural rainfall conditions, there were no significant differences in protease, urease, and nitrate reductase activity between elevated nitrogen deposition levels, although nitrite reductase activity decreased significantly compared to the control. Under increased precipitation conditions, different nitrogen levels did not significantly affect protease or nitrate reductase activity, although high levels of nitrogen loading (HN) significantly reduced nitrite reductase activity. Additional precipitation increased protease activity in the low nitrogen (LN) treatment and nitrate reductase activity in the medium and high nitrogen (MN, HN) treatments; it also reduced urease activity in the high nitrogen treatment (HN). Individually, precipitation had major effects on protease and nitrate reductase activity, while nitrogen deposition had a major effect on nitrite reductase activity, however, precipitation and nitrogen treatments did not show any significant interactive effects on all the enzyme activity. Finally, soil nitrate reductase activity was significantly, positively correlated with soil C/N ratio and NH₄⁺-N content, and positively correlated with NO₃^--N content.