Abstract: A field-simulated experiment on nitrogen deposition was conducted to investigate the effects of added nitrogen on ammonium and nitrate nitrogen, their dynamics and the role of litter in nitrogen transformation under nitrogen addition condition. The experiment was carried out in the forest system of subtropical coniferous (Cunninghamia lanceolata) and broad-leaved tree (Cinnamomum chekiangense and Castanopsis fabric) with three nitrogen levels (control (CK, 0kg/(hm²·a)), low nitrogen (LN, 30kg /(hm²·a)) and high nitrogen (HN, 100kg/(hm²·a))) and two litter treatments (retention of litter layer/isolation litter (natural status, referred to as the “retain litter”, Y) and the removal of litter layer / isolation litter (referred to as “the removal of litter”, N)) established. The results showed that, compared with the control, under simulated nitrogen deposition condition, the HN treatment significantly enhanced ammonium nitrogen content in broad-leaved forest soil, raised the amount of soil nitrate for C. fabri and C. lanceolata after three days of nitrogen addition immediately. However, the effects were not significant after three months of nitrogen addition. The dynamics of ammonium nitrogen was different before and after the simulation of nitrogen deposition and it was different from nitrate and soluble organic nitrogen (SON) after nitrogen deposition. The ammonium nitrogen contents in microorganism not increased with nitrogen deposition increasing for the broad leaved forest soil. However, compared with before fertilization, nitrogen deposition significantly increased after nitrogen deposition in summer. Compared with intact litter treatment, ammonium nitrogen in soil decreased by 17.5% and 18.9% for broad-leaved forest with litter removal before fertilization application and a small change was found for Chinese fir forest. Compared with litter intact treatment, the nitrate increased by 58.9% and 38.2% for C. chekiangense, by 7.0% and 30.0%, for C. fabric and by -17.1% and increased by 9.0% for C. lanceolata at three days and three months after the treatments with litter removal, respectively. Results indicated that there were more complex effects of litter and nitrogen addition on ammonium and nitrate nitrogen at immediate and long-term after nitrogen application, considering the similarity of nitrogen addition and precipitation case. The SON extracted from soil in broad leaved forest was highest in relative to Chinese fir forest. In order to understand the effects of nitrogen addition on immobilization of nitrogen by microorganisms, the chloroform fumigation-incubation method was used to measure the nitrogen and different forms in microorganisms. Results showed that SON content and proportion of total nitrogen in microorganism was higher in broad-leaved forest soil than it in Chinese fir forest soil. However, the content and proportion of ammonium nitrogen in Chinese fir forest soil microorganism was higher than that in broad leaved forest soil.