Abstract: This paper studies the heat exchange between the tidal sediment and seawater to explore how the tidal flats affect seawater temperature. A sediment temperature model was developed to simulate the heat flux in the tidal flats based on the data measured at a southwest Korean coastal area. The model is to simulate the spatio-temporal distribution of the vertical temperature profile of sediment in the tidal flats and heat transfer between sediment and water under scenarios with different tidal occurrences. Through the modelling scenarios, the effects to the heat flux were analyzed for the impact factors such as seasons, tidal locations, and solar-tidal phases. The modeled sediment temperature well matched the measurements. A large amount of heat exchange was found between the tidal sediment and seawater, which occurred mostly during the first three hours of interactions with a maximum heat flux rate of 398.7 W/m². Net heat was transferred from seawater to sediment during the winter months while, in opposite, net heat was transferred from sediment to seawater during the summer months. Relatively great heat exchange was found when tidal flats was inundated near noon or within three hours after noon, which can reach a value of 2.0 MJ/(m²·d). Cumulative heat fluxes decreased with reducing exposure-time rate of tidal flats. This research provides a solid background and technical supports in exploring the effects of tidal flats to the changes of the near-sea water temperature in future studies.