Abstract: Peatland is an important carbon pool in global carbon cycle. Its oligotrophic environment, ecological processes, and ecological functions are affected by nitrogen deposition. This paper reviewed the effects of nitrogen deposition on peatland ecosystems from the following aspects: (1) the production in peatland is generally nitrogen-limited, while nitrogen deposition can change the peatland soil environment by increasing nitrogen availability, altering microbial composition, increasing bacterial quantity, and improving enzyme activity; (2) in high nitrogen deposition peatland, the nitrogen interception, translocation, and tolerance abilities of Sphagnum- will be decreased, leading to the toxic effect on Sphagnum and its replacement by nitrophilous vascular plants; (3) nitrogen deposition may change the oligotrophic soil environment, and promote the productivity of peatland; (4) the increase of nitrogen supply may improve the growth of vascular plants, leading to the inferior position of Sphagnum in light competition and the alternation of interspecific relationships between Sphagnum and vascular plants; (5) nitrogen deposition will change the N/P ratio in plants, and then, affect the reproduction and regeneration of Sphagnum, which will bring about the changes of vegetation species composition, and therefore, vegetation succession in peatland; and (6) through the interaction of above and belowground biological components, nitrogen deposition will accelerate peat decomposition, and weaken the role of peatland as a carbon pool. Some issues in the present related studies were addressed, and some suggestions for the further researches were offered.