Abstract: Particle size analysis was carried out for 46 surface sediment samples collected in the inner and outer areas of Dalian Bay. Based on the results, the spatial variation in modern sedimentary dynamic environment, the sediment transportation and transportation mechanisms are studied in Dalian Bay. Exchange of sediments inside and outside the bay and its impacts are discussed. Dalian Bay has only a few sediment sources. Erosive debris from the bedrock outside the bay and the suspended sediment from the outer water are the major sources of sediments. Waves meet at the areas around capes and the Sanshan Island, forming a turbulent high-energy environment. The water channel outside the Sanshan Island is a scouring environment under the strong action of currents. The difference in current velocity between the flood and ebb currents result in the formation of double jumping components. Tidal wave is weak in Dalian Bay, and the sediment is mainly composed of suspended components. The coastal current formed by wave break is the main force keeping sediment moving along the shore of the Bay, and sediments are transported from the Laowozui Cape and Bangtao Island into the Dalian Bay. The exchange of material in the northern central bay is dominantly controlled by tidal currents, and sediments moves northward into the northern part of Dalian Bay. Although the exchange of materials is weak inside and outside Dalian Bay, the bay is a trap to capture the materials from the North Yellow Sea. The results may provide a new way of thinking to study the formation and evolution of the ancient Yellow Sea warm current.