Nitrogen (N) addition is a primary nutrient management practice to improve the productivity of degraded grasslands. Excessive N input leads to soil acidification, the increase of nitrate leaching loss and greenhouse gas emissions. This study aims to understand the response characteristics of the abundances of soil N and phosphorus (P) transformation functional genes to nitrogen and phosphorus additions, and provide reference for directionally regulating the transformation process of soil nitrogen and phosphorus, improving nutrient utilization efficiency, and reducing greenhouse gas N₂O emissions in grassland which is used mostly for haymaking. We conducted a spit-plot experiment of nutrient additions that included five N levels (0, 1.55, 4.65, 13.95, 27.9 g N m^-2 a^-1) and three P levels (0, 5.24, 10.48 g P m^-2 a^-1) and their interactions in Hulunber meadow steppe for three years (2018-2020). The abundance of genes involved in soil ammonium oxidation (amoA-AOA and amoA-AOB), denitrification (narG, nirK, nirS and nosZ) and organophosphate transformation (phoD) processes at different growth stages of plants were determined. The abundances of soil N-cycle genes were regulated by N and P additions, while the abundances of soil organophosphate transformation gene maintained constant in response to N and P additions. N addition increased the abundance of amoA-AOB and increased the relative importance of ammonia oxidizing bacteria in regulating soil nitrification rate, resulting in increasing the potential of nitrate leaching loss. P addition reduced the abundance of amoA-AOB under high N treatments, thereby decreased the potential of nitrate leaching loss. The abundance of denitrification genes (nirK and nosZ) in response to N addition varied with plant growth seasons. N addition significantly promoted the abundance of nirK and nosZ in August, thereby increasing gaseous N loss potential. Excessive N input might promote the process of soil ammonia oxidation and denitrification, and increase the potential of nitrate leaching loss and gaseous N loss. P addition may reduce the potential of nitrate leaching loss and play a potential role in improving N utilization efficiency.