The Suaeda salsa marsh in the high tidal flat of the northern Yellow River estuary was selected as the study object. In the first year, in situ experiment of different nitrogen (N) loadings (N0, no N import treatment; N1, low N import treatment; N2, middle N import treatment; and N3, high N import treatment) was conducted. At the end of the growing season, litters with different substrate qualities (NL0, NL1, NL2, and NL3) were sampled from different N import plots. In the second year, these litters were placed in the corresponding N import plots, and N loadings were continuously conducted as the same with the first year. The objective of this study was to investigate the effect of exogenous nitrogen enrichment on decomposition and sulfur (S) release of S. salsa litters. The results showed that the decomposition rates of S. salsa litters generally followed the order of NL1 > NL3 > NL2 > NL0, indicating that, as N was continuously imported, the alteration of substrate quality promoted litter decomposition and the promotion was particularly obvious in the low N treatment (N1), which was mainly related to alterations in C/N ratios during decomposition. The total sulfur (TS) contents in litters of different N loadings showed different fluctuations, which were opposite to the corresponding C/S ratios, indicating that the C/S ratio was the main factor controlling the variations in TS contents of different litters during decomposition. For litters with different substrate qualities, the net release of S was observed throughout the decomposition process and the release amounts were generally in the order of NL3 > NL1 > NL2 > NL0, indicating that, as N was continuously imported, alterations in litter quality stimulated the release of S and the stimulation was predominant in the high N treatment (N3). This study showed that increasing N loading in the intertidal zone of the Yellow River estuary would alter the substrate quality of S. salsa litters and continuous N loading would promote S returning from the litters. As a result, the S biological cycling rate in S. salsa marsh would be accelerated.