Abstract: Iron (Fe) is an essential micronutrient for the growth of marine phytoplankton and a key factor to affect marine primary productivity. Dissolved reactive iron (DR_Fe), one of the main components of dissolved Fe, is closely related to the absorption of marine organisms. In this paper, the variation characteristics of DR_Fe concentration at high tide and low tide were studied by continuous monitoring at Yellow Sea coast for 30 days. The effect of tidal action on DR_Fe concentration was analyzed, and the relationship between DR_Fe concentration and physicochemical parameters of seawater was further discussed. This study showed that the DR_Fe concentration at high tide was slightly higher than that at low tide, with a maximum concentration difference of 2.32 nmol/L and a minimum concentration difference of 0.44 nmol/L. The monthly variation of DR_Fe concentration was not significant in May, ranging from 4.06 to 8.34 nmol/L, with an average concentration of 5.70 nmol/L. DR_Fe concentrations were higher at the beginning of the month and then gradually declined. The increase of seawater temperature will promote the growth of phytoplankton and increase of chlorophyll a content, which will accelerate the consumption of DR_Fe.