Abstract: This paper attempts to re-analyze the depositional system of river deltas from the perspective of sediment dynamics. According to the definition that "river deltas are concentrated deposits associated with the same river flowing into the sea", the traditional three-end-member classification diagram based on runoff, tides and waves does not seem to have covered all types of deltas. Coastal embayment morphology, shelf circulation and sea level changes are also important; they are related to the end-member forms of embayment filling delta, distal mud and shelf edge delta, respectively. Sediment gravity flow is also a factor that cannot be neglected for some stages of delta evolution. Hence, the above factors may be combined by an integrated modeling system to define a delta morphological spectrum, which is beneficial to the study on the process-product relationships. The relevant scientific issues that are worth exploring include: (1) any criteria to differentiate between the clinoforms of subaqueous delta and the distal mud, to be used in the analysis of deltaic deposits within the stratigraphic sequence, e.g., the classification of shelf edge deltas; (2) the completeness of the sedimentary record, in relation to the spatial and temporal distribution patterns of the various components of a delta system; and (3) the relationship between delta evolution (and its ultimate magnitude in particular) and sediment budgeting processes.