Mangrove swamp plays an important role in the maintenance of ecological balance in tropical-subtropical coastal regions, as well as in the global carbon cycle. The grain size characteristic and sedimentary rate of two mangrove swamps were studied. The grain size and proportion of storm deposit were determined, and the factors that influenced storm sediment inputting flux were analyzed. The variation of mangrove swamp accretion rate in response to climate change was also studied. The main conclusions are as follows. 1) The inputted sediments were silt and clay in normal weather condition during tidal process, while the sand component in mangrove swamp sediment was likely inputted by storms. In mangrove swamp sediment, the proportion of storm deposit was 56% for mangrove swamp of the Nanliujiang River estuary and 73% for Daguansha mangrove swamp. 2) The sedimentation rate of mangrove swamp was positive related to typhoon landfall frequency rather than rain fall. 3) The storm energy was higher in Daguansha mangrove swamp than in the Nanliujiang River estuary, likely attributing to its open coastline shape with narrow width in tidal zone and mangrove belt, which may deduce more storm deposit inputted and higher sedimentary rate.