Abstract: Objectives: The deformation of the river estuary sluice gate may be slightly affected by the tidal fluctuations, and studying the sluice gate's response to tidal deformation is of great significance for the safety and maintenance of the sluice gate. GNSS is a significant tool for deformation monitoring, commonly used for high-precision deformation monitoring of dams or extraction of vibrational characteristics of bridges. However, existing GNSS monitoring mode is inadequate for identifying the characteristics of tidal response signals. Methods: In this study, the Cao'e River Sluice was selected as the research subject. GNSS base and monitoring stations were set up to observe the sluice's deformation. And a method utilizing GNSS-based monitoring techniques was proposed to extract sub-millimeter-level deformation signals with a period of several hours, aimed at identifying the tidal response of the river estuary sluice gate. Results: The results show that due to tidal fluctuations, the Cao’e River Sluice has the greatest response to the larger M2 and S2 partial tides, but the response signal is weak, with the same frequency amplitude not exceeding 1.5 mm in the U direction, and not exceeding 1 mm in the X and Y directions. Overall, the sluice's response to each partial tide is linearly positively correlated in terms of amplitude size, but an excessive response to individual partial tides (such as S4, K1) has occurred, which may be caused by other signals of the same frequency. Conclusions: Using a 5-minute sliding step and a 2-hour solution window can effectively retain the characteristics of the tidal response. This method facilitates the accurate monitoring and assessment of the sluice gate's response to tidal influences, thereby enhancing the safety and maintenance strategies for estuarine sluice structures.