Abstract: Based on the field observation data in spring of 2016 in the Mulan Estuary and its adjacent seas, hydrological environment factors, such as temperature, salinity and turbidity were analyzed. And the characteristics and mechanism of suspended sediment transport in the Nanri waterway were studied using the mechanism decomposition method. Results show that the changes in temperature and salinity in the Xinghua Bay and its adjacent seas in spring are jointly controlled by the Mulan River runoff, the Zhejiang-Fujian Coastal Current and the Taiwan Warm Current. The offshore water in southeast Xinghua Bay is dominated by Taiwan Warm Current characterized by high temperature and high salinity, while the nearshore water in the northwest of the bay is significantly affected by the Zhejiang-Fujian Coastal Current featured by low temperature and low salinity. Suspended sediment concentration in Xinghua Bay and its adjacent seas is relatively low. Offshore sediments can be transported into Xinghua Bay through the Nanri waterway, but the net sediment flux is quite limited, only 0.32×10^-4 kg/(m·s). The advection and tidal pumping are the major mechanisms for net sediment transport in the waterway, the resuspension of bottom sediment is significant, and the shear diffusion effect cannot be ignored.