Abstract: Sediment transport in tidal estuaries is complex and changeable. How to scientifically classify the forms of sediment transport and evaluate its impact on channel sedimentation is the key to clarify the source of sediments deposited in the channel and formulate channel siltation reduction measures. In this paper, a new method identifying three forms of sediment transport, that is the bed load (BL), the suspended load (SL) and the bed-suspended conversion load (BSCL), was proposed based on analyzing the grain size of surficial bed sediment (SBS) and near bottom suspended sediment (NBSS). The sediment samples were collected along the Deepwater Navigational Channel (DNC) in the Yangtze Estuary (YE) during the flood and dry seasons of 2015 and 2018, and the contributions of three forms of sediment transport to the channel sedimentation was quantified. The results show that the upper turning point of grain size cumulative frequency curve is able to well represent the sediment transport form transition from BL to SL. There exists a significant sediment exchange between SBS and NBSS at the South Channel (SC) as well as the North Passage (NP) of YE. The sediment transport in DNC are not only in forms of BL and SL, but also in BSCL, which accounts for the proportion of 50% to 60% of the channel sedimentation. The contribution of BL to the channel deposition at SC segment of DNC in flood and dry season are 36% and 26% respectively, which is higher than that of SL occupying 6% and 13%. In contrast, the contribution of SL to the channel deposition at NP segment of DNC ranges from 44% to 48%, which is much higher than that of BL only accounting for 3% to 6%. The proposed method based on the grain size analysis provides a new sight on understanding the characteristics of sediment movement in tidal estuary and identifying the source of sediments deposited in the channel.