Abstract: Tidal flats, situated within the interface of terrestrial, marine, atmospheric and anthropogenic influences, exhibit high sensitivity to human disturbance. However, it remains unclear how regime shifts in embayment-type tidal flat systems evolve under intense human activities. This study examines the driving processes of human activities on the evolution of the tidal flats in the Luoyangjiang Estuary by analyzing two sediment cores collected from different sites in the estuary. Results indicate that sediments from both the upstream and downstream tidal flats are primarily composed of fine-grained material, mainly clayey silt, with mean grain sizes of 5.87 Φ ～ 7.29 Φ (mean: 6.85 Φ) and 5.17 Φ ～ 7.18 Φ (mean: 6.32 Φ), respectively. The average sedimentation rates for the two core samples were 2.97 cm/a and 3.94 cm/a. Following the invasion of Spartina alterniflora, the average sedimentation rate increased from 1.93 cm/a to 3.71 cm/a in the upstream tidal flat and from 1.25 cm/a to 4.58 cm/a in the downstream tidal flat. Overall, the tidal flats of the Luoyangjiang Estuary experienced stable and continuous accretion; however, large-scale land reclamation (including the construction of a sluice gate upstream in the Luoyangjiang Estuary) substantially modified sediment grain-size composition, and the rapid expansion of Spartina alterniflora further accelerated sedimentation rates. The findings of this study provide a scientific basis for future ecological conservation and restoration planning of the tidal flat ecosystem in the Luoyangjiang Estuary.