Abstract: The response of Yangtze River subaquatic delta to river sediment decline has attracted more and more attention in recent years. In this paper, grain sizes and radiometric ²¹⁰Pb and ¹³⁷Cs of the cores in different areas of the subaquatic delta were analyzed to explore the response to river sediment decline and change of hydrodynamic force. The results show that grain sizes of core CDZS10 sediments are much coarser than those of the other three cores which might be closely related to the block of north branch of Yangtze River in the estuary after 1954. In terms of sediment composition the authors found grain size coarsening up from 1.2m (1979) in Core CDZS10 which might be an obvious response to significant sediments supply decline of the Yangtze River after the 1980's. In addition, the block of north branch and impoundment hasled to the mud region moving southward and extending to Hangzhou Bay and Shengsi Islands.