This paper reviews nitrogen cycling in marine sediments and consists of three parts： 1. Nitrogen Cycling Processes in Marine Sediments (1) Nitrogen and primary production Nitrogen regenerated from marine sediments can contribute largely to primary production. About 30%-80% of nitrogen consumed by phytoplankton is attributed to sediment mineralization and NH4+ (ammonium) is the preferred phase utilized. Benthic heterotrophic bacteria have a large impact on nitrogen cycling and can act as net N consumers sometimes. (2) Early diagenesis and nutrients loss Early diagenesis includes oxic and anoxic mineralization. Part of the regenerated NH4+ can be transformed into N2 by the nitrification-denitrification coupling, which leads to nutrient loss from the marine ecosystem. NH4+ adsorption in sediment is another pathway for nutrient loss. (3) Nitrogen cycling and the controlling factors NH4+ released from sediments can be assimilated by benthic organisms and diffuse to overlying water or be oxdized into NO3- (nitrate). The role of sediment as a source or sink for nitrogen in seawater is governed by the relative rates of ammonium, nitrate and N2 production. The nitrogen cycling process varies with time and space and the controlling factors includes: temperature, organic matter content, benthic bioturbation. etc. (4) The formation and function of particulate nitrogen PN (particulate nitrogen) is mainly formed biogenically. Amino acids account for 30%-60% of the organic nitrogen in particulates. PN can be mineralized or uptaken during sedimentation. The most attractive focus on PN is its function in the marine ecosystem food web. (5) Nitrogen cycling and other biogenic element cyclings Nitrogen cycling is in closely correlated with C and P cycling. The efficiency of N and P cycling increases with increased organic carbon loading in sediments. The atomic ratio of C, N, P in sediment deviates from the Redfield ratio of 106: 16: 1 and the former is a very important parameter in nitrogen cycling model construction. 2. Methods for nitrogen cycling research Research on nitrogen cycling in marine sediments usually focuses on two aspects: nitrogen in sediment and nitrogen in porewater, on which much work has been done on the pore-water. The rates of mineralization, nitrification, denitrification and the exchange fluxes between sediment and overlying water can be measured. Acetylene (C2H2) inhibition technique and 15N tracer technique are most widely used. Analysis for sediment solid is not sufficient, only NH4+ adsorption concentration and total organic nitrogen can be measured. 3. Perspectives on nitrogen cycling research It has been known that particulate size and organic matter composition in sediments can control nitrogen cycling significantly. So more attention should be paid to these two factors in further research.