[Objective] The responses of bryophytes' photosynthesis to nitrogen addition in the process of its dehydration were studied in order to demonstrate how it will respond to nitrogen deposition and to provide relevant theoretical knowledge for management of desert ecosystems in arid or semi-arid region.[Methods] The dominant bryophytes, Bryum pachytheca in Mu Us desert was selected to examine the responses of bryophytes' photosynthesis to nitrogen addition with eight levels.[Results] The net photosynthetic rates of bryophytes(P_n) increased when nitrogen addition was less than 0.2 g/(m²·a). When nitrogen addition was over 0.2 g/(m²·a), the responses of P_n varied under different water condition. It was enhanced under high levels of water content, and was suppressed under low levels. In terms of bryophytes' photosynthetic carbon sequestration capacity in tested site, the optimal adding amount of nitrogen was 0.2 g/(m²·a). At this addition amount, carbon fixed by bryophytes' photosynthesis was doubled as compared with that without adding nitrogen.[Conclusion] Nitrogen increment from deposition can strongly influence photosynthesis and carbon sequestration capacity of bryophytes in arid and semi-arid regions.