Abstract: Modaomen estuary is one of the main outlets of the Zhujiang (Pearl) River. Since the 1980s, large-scale human activities such as riverbed sand dredging and estuary regulation, had lead to some changes of channel topography and hydrodynamic. Based on field data such as topographic data and water data from different years, this paper provide some primarily conclusions as follows: (1)large-scale sand dredging at Modaomen waterway resulted in riverbed deepening and channels volume increasing. Due to estuary regulation, the shallow sea at Modaomen estuary turned into two waterways regulated by artificial banks. As a result, water area and channel volume were reduced. Riverbed of the waterway became deepening. (2) During dry season in recent years, Topographic change in Modaomen waterway lead to tidal dynamic enhancing apparently at Zhuyin station, the upper reaches of Modaomem estuary, with low water level dropping, tidal range increasing and tidal influx increasing. As well, at Dahengqin station, near the outlet of Modaomen estuary, water level rise with tidal assembly and tidal range decreasing. Phase difference between Dahengqin and Zhuyin reduced, and tidal wave propagation velocity increased with saline water intruding frequently.