Microplastics (MPs) affect the fractionation of cadmium (Cd) by altering physicochemical properties of sediment. However, differences in the effect of drying-wetting cycles on the bioavailability of heavy metals and dissolved organic matter (DOM) in sediment amended with MPs remain unclear. In this study, we investigated the influence of polystyrene (PS), polylactic acid (PLA), and tire wear particles (TWPs) at concentrations of 0.5% and 5% (w/w) on Cd fractionation and DOM properties of sediment under drying-wetting alternation conditions. The results showed that the surface of MPs displayed obvious increase in surface roughness and oxygen-containing functional groups after drying-wetting cycles. At the end of drying-wetting cycles, 0.5% and 5% MPs significantly decreased the sediment pH. And 5% PLA MPs and TWPs significantly increased the content of dissolved organic carbon (DOC). Besides, Cd bioavailability showed a slight decrease under wet conditions. However, 5% PLA MPs significantly increased F1 fraction by 7.82%-13.50%, which may be related to the release of additives. The aromaticity and humification degree of sediment-derived DOM were improved under drying-wetting alternation conditions. Further correlation analysis indicated that MPs indirectly affected Cd fractionation by influencing the sediment DOM properties. This study provides a new perspective for understanding the influence of MPs on the relationship between DOM and heavy metals in riparian sediments under typical hydrological condition.