Abstract: Based on the measured data of hydrology and sediment in January 2016, the hydrodynamic environment and sediment environment of the Yong River mouth and its adjacent sea waters are analysed in this paper. Some conclusions are achieved as follows: ① The differences among highest water levels along the river are not significant, while the lowest water level reduces along the river; the tidal power of the sea waters in the northwest of the mouth is stronger than the tidal power of the southeastern sea waters. ②The flow velocities gradually increase from the upper section to the lower along the river, and their distribution around the mouth is characterized by being stronger in the north side and weaker in the south side. Around the estuary, the flow velocities in the river and in the sea waters are similar. ③The sediment concentration of the Yong River first increases and then decreases along the river. There is a higher sediment concentration in the northwest of the estuary than that in the southeast. ④In the Yong River there are two peak values of the sediment concentration during the same tidal cycle, which appear respectively 1-2 hours after the maximum flood and the maximum ebb. Different from what it is like in the river, there are two types of sediment concentration in the sea area outside the estuary, namely the single-peak and the double-peak.