Abstract: Based on the survey data of macrobenthos in the intertidal flat of Luoyuan Bay in 2009, and by using Brey’s empirical formula, this paper estimated the macrobenthos secondary productivity, production/biomass (P/B) ratio, and their spatiotemporal distribution patterns in the flat. The annual secondary productivity and P/B ratio of the macrobenthos in the flat were estimated as 18.58 g AFDM （ash free dry mass）·m^-2 ·a^-1 and 0.97, respectively, and the secondary productivity in the Spartina alterniflora marshes of the upper intertidal flat (8.97g AFDM·m^-2· a^-1) was much lower than that in the bare flat of the lower intertidal zone (28.19 g AFDM·m^-2·a^-1). Since the introduction of S. alterniflora by the end of the 1980s, the secondary productivity of the macrobenthos in the flat had increased about 4 folds.  Musculus senhousei, which  inhabited in the lower bare flat, contributed 66.4% of the total macrobenthos secondary productivity in the entire intertidal flat. If the contribution from M. senhousei was not taken into account, the macrobenthos secondary productivity in the salt marshes would be significantly higher than that in the bare flat, and the macrobenthos secondary productivity in the intertidal flat would have less change. The successful colonization of M. senhousei was partly attributed to the changes of sediment composition enhanced by S. alterniflora due to its capability in trapping fine-grained materials; this species’ feeding activities result in a remarkable increase of sediment chlorophyll a content. There was a significant positive correlation between the secondary productivity of macrobenthos and the sediment chlorophyll a and/or organic matter contents. These findings suggested that salt marshes had effects on the coastal wetland ecosystem via a number of physical and biological mechanisms.