This study aimed to clarify the effects of the long-term application of reduced chemical fertilizers combined with Chinese milk vetch on the adsorption and desorption characteristics of ammonium nitrogen in soil. A 13-year long-termpositioning test was conducted using five treatments:no fertilizer(CK)，fertilizer only(CF)，22500 kg/hm² Chinesemilk vetch + 80% fertilizer(G+0.8CF)，22500 kg/hm²Chinese milk vetch + 60% fertilizer(G+0.6CF)，and 22500 kg/ hm²Chinese milk vetch + 40% fertilizer(G+0.4CF). The ammonium nitrogen adsorption and desorption characteristicsof soil subjected to different fertilization treatments were examined，and the relationship between soil ammonium nitrogen adsorption and desorption characteristic parameters and soil physicochemical properties was analyzed. The results showed that Langmuir’s isotherm adsorption equation demonstrated a good fit with the adsorption characteristics of soil ammonium nitrogen(R2=0.9969–0.9979，P<0.01). Compared with those in CKsoil，the maximum adsorption amount and maximum buffering capacities of ammonium nitrogen in soil subjected to Chinese milk vetch + reduced fertilizer treatment decreased by 4.85%–13.46% and 4.55%–7.36%，respectively. The average desorption amount and desorption rate of soil ammonium nitrogenwere in the followingorder:G+0.8CF > G+0.6CF > G+0.4CF > CF > CK. Compared with those of CKsoil，the total nitrogen and available nitrogen concentrations of soil treated with Chinese milk vetch combined with reduced fertilizer increased by 19.42%–46.60% and 15.24%–25.88%，respectively. Correlation analyses revealed that the desorption rate had significantly positive correlations with soil total nitrogen and available nitrogen and a significantly negative correlation with soil pH. Redundancy analysis demonstrated that pH and available nitrogen were the main factors causing the differences in adsorptionand desorption characteristic parameters of soil ammoniumnitrogen，accounting for 56.7% and 39.1% of allvariations，respectively( P<0.05). In summary，long -term Chinese milk vetch application coupled with reduced chemical fertilizerusage reduced soil adsorption of ammoniumnitrogen，increased soil desorption of ammoniumnitrogen，reduced soil nitrogenfixation，and improved nitrogen availability. Considering the adsorption and desorption characteristics of soil ammoniumnitrogen and soil nutrientcontent，treatments involving a chemical fertilizer reduction of 20% –40% combined with 22500 kg/hm² of Chinese milk vetch were potentially suitable for the southern Henan rice area.