Abstract: Based on the grain size test data of 30 surface sediments in Yangma Island sea area in Bohai Sea, Yantai, the grain size parameters were calculated and end members were specified. The sedimentary dynamic environment and material source of sediments were analyzed by combining regional hydrodynamics and shoreline types. Results show that the average grain size (Φ) of the marine sediment gradually increased from river estuary off coast seaward, from moderately to poorly sorted, the skewness turned extremely positive, and the kurtosis was from mesokurtic to leptokurtic. Four single-peak end-member components were recognized from the grain size data, namely, EM1, EM2, EM3, and EM4 in the size ranges of 2.75～8.75, 3.00～6.25, 2.25～4.25, and 1.50～3.75, respectively. The EM1 represented a sedimentary environment in deep water and weak hydrodynamics, and the source of the material was the fine-grained material from Yellow River carried out by the Yellow Sea littoral currents. The EM2 end-member represented a weak hydrodynamic sedimentary environment under the effect of tidal wave superposition, and the material source was the mixture of Yellow River inlet sediment carried by the Yellow Sea littoral current and the debris produced by seawater erosion of bedrock coast. The EM3 end-member represented the sedimentary environment with strong hydrodynamic force under the influence of tidal current, wave superposition and channel, and the material source was the debris produced by the inlet river-carried sediments and the mix of seawater erosion of sand and mud coast. The EM4 end-member represented a strong hydrodynamic sedimentary environment under the joint action of seawater and river hydrodynamics, and the source of material was the sediment carried by the river into the sea, mixed with the sand and mud coast eroded by seawater, and the debris that generated from human activities.